β-L-2′-deoxy-nucleosides for the treatment of hepatitis B

ABSTRACT

This invention is directed to a method for treating a host infected with hepatitis B comprising administering an effective amount of an anti-HBV biologically active 2′-deoxy-β-L-erythro-pentofuranonucleoside or a pharmaceutically acceptable salt or prodrug thereof, wherein the 2′-deoxy-β-L-erythro-pentofuranonucleoside has the formula: 
                         
wherein R is selected from the group consisting of H, straight chained, branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl, CO-aryloxyalkyl, CO-substituted aryl, alkylsulfonyl, arylsulfonyl, aralkylsulfonyl, amino acid residue, mono, di, or triphosphate, or a phosphate derivative; and BASE is a purine or pyrimidine base which may be optionally substituted. The 2′-deoxy-β-L-erythro-pentofuranonucleoside or a pharmaceutically acceptable salt or prodrug thereof may be administered either alone or in combination with another 2′-deoxy-β-L-erythro-pentofuranonucleoside or in combination with another anti-hepatitis B agent.

This application is a continuation application of U.S. patentapplication Ser. No. 11/558,288, filed on Nov. 9, 2006, now pending,which is a continuation application of U.S. patent application Ser. No.11/230,944, filed on Sep. 20, 2005, now abandoned, which is acontinuation of Ser. No. 10/437,802, filed May 13, 2003, issued as U.S.Pat. No. 6,946,450, which is a continuation application of U.S. patentapplication Ser. No. 10/022,148, filed Dec. 14, 2001, issued as U.S.Pat. No. 6,566,344, which is a continuation of U.S. patent applicationSer. No. 09/459,150, filed Dec. 10, 1999, issued as U.S. Pat. No.6,444,652, which is a continuation in part application of U.S. patentapplication Ser. No. 09/371,747, filed on Aug. 10, 1999, issued as U.S.Pat. No. 6,395,716, which claims priority to U.S. provisionalapplication Nos. 60/096,110, filed on Aug. 10, 1998 and 60/131,352,filed on Apr. 28, 1999.

BACKGROUND OF THE INVENTION

This invention is in the area of methods for the treatment of hepatitisB virus (also referred to as “HBV”) that includes administering to ahost in need thereof, either alone or in combination, an effectiveamount of one or more of the active compounds disclosed herein, or apharmaceutically acceptable prodrug or salt of one of these compounds.

HBV is second only to tobacco as a cause of human cancer. The mechanismby which HBV induces cancer is unknown, although it is postulated thatit may directly trigger tumor development, or indirectly trigger tumordevelopment through chronic inflammation, cirrhosis, and cellregeneration associated with the infection.

Hepatitis B virus has reached epidemic levels worldwide. After a two tosix month incubation period in which the host is unaware of theinfection, HBV infection can lead to acute hepatitis and liver damage,that causes abdominal pain, jaundice, and elevated blood levels ofcertain enzymes. HBV can cause fulminant hepatitis, a rapidlyprogressive, often fatal form of the disease in which massive sectionsof the liver are destroyed.

Patients typically recover from acute hepatitis. In some patients,however, high levels of viral antigen persist in the blood for anextended, or indefinite, period, causing a chronic infection. Chronicinfections can lead to chronic persistent hepatitis. Patients infectedwith chronic persistent HBV are most common in developing countries. Bymid-1991, there were approximately 225 million chronic carriers of HBVin Asia alone, and worldwide, almost 300 million carriers. Chronicpersistent hepatitis can cause fatigue, cirrhosis of the liver, andhepatocellular carcinoma, a primary liver cancer.

In western industrialized countries, high risk groups for HBV infectioninclude those in contact with HBV carriers or their blood samples. Theepidemiology of HBV is very similar to that of acquired immunedeficiency syndrome (AIDS), which accounts for why HBV infection iscommon among patients with AIDS or AIDS related complex. However, HBV ismore contagious than HIV.

However, more recently, vaccines have also been produced through geneticengineering and are currently used widely. Unfortunately, vaccinescannot help those already infected with HBV. Daily treatments withα-interferon, a genetically engineered protein, has also shown promise,but this therapy is only successful in about one third of treatedpatients. Further, interferon cannot be given orally.

A number of synthetic nucleosides have been identified which exhibitactivity against HBV. The (−)-enantiomer of BCH-189, known as 3TC,claimed in U.S. Pat. No. 5,539,116 to Liotta, et al., has been approvedby the U.S. Food and Drug Administration for the treatment of hepatitisB. See also EPA 0 494 119 A1 filed by BioChem Pharma, Inc.

Cis-2-hydroxymethyl-5-(5-fluorocytosin-1-yl)-1,3-oxathiolane (“FTC”)exhibits activity against HBV. See WO 92/15308; Furman, et al., “TheAnti-Hepatitis B Virus Activities, Cytotoxicities, and Anabolic Profilesof the (−) and (+) Enantiomers ofcis-5-Fluoro-1-[2-(Hydroxymethyl)-1,3-oxathiolane-5-yl]-Cytosine”Antimicrobial Agents and Chemotherapy, December 1992, page 2686-2692;and Cheng, et al., Journal of Biological Chemistry, Volume 267(20),13938-13942 (1992).

von Janta-Lipinski et al. disclose the use of the L-enantiomers of3′-fluoro-modified β-2′-deoxyribonucleoside 5′-triphosphates for theinhibition of hepatitis B polymerases (J. Med. Chem., 1998, 41,2040-2046). Specifically, the 5′-triphosphates of3′-deoxy-3′-fluoro-β-L-thymidine (β-L-FTTP),2′,3′-dideoxy-3′-fluoro-β-L-cytidine (β-L-FdCTP), and2′,3′-dideoxy-3′-fluoro-β-L-5-methylcytidine (β-L-FMethCTP) weredisclosed as effective inhibitors of HBV DNA polymerases.

WO 96/13512 to Genencor International, Inc. and Lipitek, Inc. disclosesthat certain L-ribofuranosyl nucleosides can be useful for the treatmentof cancer and viruses. Specifically disclosed is the use of this classof compounds for the treatment of cancer and HIV.

U.S. Pat. Nos. 5,565,438, 5,567,688 and 5,587,362 (Chu, et al.) disclosethe use of 2′-fluoro-5-methyl-β-L-arabinofuranolyluridine (L-FMAU) forthe treatment of hepatitis B and Epstein Barr virus.

Yale University and University of Georgia Research Foundation, Inc.disclose the use of L-FddC (β-L-5-fluoro-2′,3′-dideoxycytidine) for thetreatment of hepatitis B virus in WO 92/18517.

The synthetic nucleosides β-L-2′-deoxycytidine (β-L-2′-dC),β-L-2′-deoxythymidine (β-L-dT) and β-L-2′-deoxyadenosine (β-L-2′-dA),are known in the art. Antonin Holy first disclosed β-L-dC and β-L-dT in1972, “Nucleic Acid Components and Their Analogs. CLIII. Preparation of2′-deoxy-L-Ribonucleosides of the Pyrimidine Series,” Collect. Czech.Chem. Commun. (1972), 37(12), 4072-87. Morris S. Zedeck et al. firstdisclosed β-L-dA for the inhibition of the synthesis of induced enzymesin Pseudomonas testosteroni, Mol. Phys. (1967), 3(4), 386-95.

Certain 2′-deoxy-β-L-erythro-pentofuranonucleosides are known to haveantineoplastic and selected antiviral activities. Verri et al. disclosethe use of 2′-deoxy-β-L-erythro-pentofuranonucleosides as antineoplasticagents and as anti-herpetic agents (Mol. Pharmacol. (1997), 51(1),132-138 and Biochem. J. (1997), 328(1), 317-20). Saneyoshi et al.demonstrate the use of 2′-deoxy-L-ribonucleosides as reversetranscriptase (I) inhibitors for the control of retroviruses and for thetreatment of AIDS, Jpn. Kokai Tokkyo Koho JP06293645 (1994).

Giovanni et al. tested 2′-deoxy-β-L-erythro-pentofuranonucleosidesagainst partially pseudorabies virus (PRV), Biochem. J. (1993), 294(2),381-5.

Chemotherapeutic uses of 2′-deoxy-β-L-erythro-pentofuranonucleosideswere studied by Tyrsted et al. (Biochim. Biophys. Acta (1968), 155(2),619-22) and Bloch, et al. (J. Med. Chem. (1967), 10(5), 908-12).

β-L-2′-deoxythymidine (β-L-dT) is known in the art to inhibit herpessimplex virus type 1 (HSV-1) thymidine kinase (TK). Iotti et al., WO92/08727, teaches that β-L-dT selectively inhibits the phosphorylationof D-thymidine by HSV-1 TK, but not by human TK. Spaldari et al.reported that L-thymidine is phosphorylated by herpes simplex virus type1 thymidine kinase and inhibits viral growth, J. Med. Chem. (1992),35(22), 4214-20.

In light of the fact that hepatitis B virus has reached epidemic levelsworldwide, and has severe and often tragic effects on the infectedpatient, there remains a strong need to provide new effectivepharmaceutical agents to treat humans infected with the virus that havelow toxicity to the host.

Therefore, it is an object of the present invention to provide newmethods and compositions for the treatment of human patients or otherhosts infected with hepatitis B virus.

SUMMARY OF THE INVENTION

A method for the treatment of hepatitis B infection in humans and otherhost animals is disclosed that includes administering an effectiveamount of a biologically active2′-deoxy-β-L-erythro-pentofuranonucleoside (referred to alternativelyherein as a β-L-d-nucleoside or a β-L-2′-d-nucleoside) or apharmaceutically acceptable salt or prodrug thereof, administered eitheralone or in combination, optionally in a pharmaceutically acceptablecarrier. The term 2′-deoxy, as used in this specification, refers to anucleoside that has no substituent in the 2′-position.

The disclosed 2′-deoxy-β-L-erythro-pentofuranonucleosides, orpharmaceutically acceptable prodrugs or salts or pharmaceuticallyacceptable formulations containing these compounds are useful in theprevention and treatment of hepatitis B infections and other relatedconditions such as anti-HBV antibody positive and HBV-positiveconditions, chronic liver inflammation caused by HBV, cirrhosis, acutehepatitis, fulminant hepatitis, chronic persistent hepatitis, andfatigue. These compounds or formulations can also be usedprophylactically to prevent or retard the progression of clinicalillness in individuals who are anti-HBV antibody or HBV-antigen positiveor who have been exposed to HBV.

In one embodiment of the present invention, the2′-deoxy-β-L-erythro-pentofuranonucleoside derivative is a compound ofthe formula:

wherein R is selected from the group consisting of H, straight chained,branched or cyclic alkyl, CO-alkyl, CO-aryl, CO-alkoxyalkyl,CO-aryloxyalkyl, CO-substituted aryl, alkylsulfonyl, arylsulfonyl,aralkylsulfonyl, amino acid residue, mono, di, or triphosphate, or aphosphate derivative; and BASE is a purine or pyrimidine base which mayoptionally be substituted.

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-2′-deoxyadenosine or a pharmaceutically acceptablesalt or prodrug thereof, of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-2′-deoxycytidine or pharmaceutically acceptable saltor prodrug thereof of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-2′-deoxyuridine or pharmaceutically acceptable salt orprodrug thereof of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-2′-deoxyguanosine or pharmaceutically acceptable saltor prodrug thereof of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-2′-deoxyinosine or pharmaceutically acceptable salt orprodrug thereof of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative is β-L-thymidine or a pharmaceutically acceptable salt orprodrug thereof of the formula:

wherein R is H, mono, di or tri phosphate, amino acid residue, acyl, oralkyl, or a stabilized phosphate derivative (to form a stabilizednucleotide prodrug).

In another embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleoside isadministered in alternation or combination with one or more other2′-deoxy-β-L-erythro-pentofuranonucleosides or one or more othercompounds which exhibit activity against hepatitis B virus. In general,during alternation therapy, an effective dosage of each agent isadministered serially, whereas in combination therapy, an effectivedosage of two or more agents are administered together. The dosages willdepend on absorption, inactivation, and excretion rates of the drug aswell as other factors known to those of skill in the art. It is to benoted that dosage values will also vary with the severity of thecondition to be alleviated. It is to be further understood that for anyparticular subject, specific dosage regimens and schedules should beadjusted over time according to the individual need and the professionaljudgment of the person administering or supervising the administrationof the compositions.

In another embodiment, the invention includes a method for the treatmentof humans infected with HBV that includes administering an HBV treatmentamount of a prodrug of the disclosed2′-deoxy-β-L-erythro-pentofuranonucleoside derivatives. A prodrug, asused herein, refers to a compound that is converted into the nucleosideon administration in vivo. Nonlimiting examples include pharmaceuticallyacceptable salt (alternatively referred to as “physiologicallyacceptable salts”), the 5′ and N⁴(cytidine) or N⁶(adenosine) acylated(including with an amino acid residue such as L-valinyl) or alkylatedderivatives of the active compound, or the 5′-phospholipid or 5′-etherlipids of the active compound.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 illustrates a general process for obtainingβ-L-erythro-pentafuranonucleosides (β-L-dN) using L-ribose or L-xyloseas a starting material.

FIG. 2 is a graph which illustrates the metabolism of L-dA, L-dC, andL-dT in human Hep G2 cells in terms of accumulation and decay. The cellswere incubated with 10 μM of compound.

FIG. 3 is a graph which illustrates the antiviral effect of β-L-dA,β-L-dT and β-L-dC in the woodchuck chronic hepatitis model.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “substantially in the form of a single isomer”or “in isolated form” refers to a2′-deoxy-β-L-erythro-pentofuranonucleoside that is at leastapproximately 95% in the designated stereoconfiguration. In a preferredembodiment, the active compound is administered in at least this levelof purity to the host in need of therapy.

As used herein, the term hepatitis B and related conditions refers tohepatitis B and related conditions such as anti-HBV antibody positiveand HBV-positive conditions, chronic liver inflammation caused by HBV,cirrhosis, acute hepatitis, fulminant hepatitis, chronic persistenthepatitis, and fatigue. The method of the present invention includes theuse of 2′-deoxy-β-L-erythro-pentofuranonucleoside derivativesprophylactically to prevent or retard the progression of clinicalillness in individuals who are anti-HBV antibody or HBV-antigen positiveor who have been exposed to HBV.

As used herein, the term alkyl, unless otherwise specified, refers to asaturated straight, branched, or cyclic, primary, secondary, or tertiaryhydrocarbon, typically of C₁ to C₁₈, preferably C₁ to C₆ andspecifically includes but is not limited to methyl, ethyl, propyl,butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, t-butyl,isopentyl, amyl, t-pentyl, cyclopentyl, and cyclohexyl.

As used herein, the term acyl refers to moiety of the formula —C(O)R′,wherein R′ is alkyl; aryl, alkaryl, aralkyl, amino acid residue,heteroaromatic, alkoxyalkyl including methoxymethyl; arylalkyl includingbenzyl; aryloxyalkyl such as phenoxymethyl; aryl including phenyloptionally substituted with halogen, C₁ to C₄ alkyl or C₁ to C₄ alkoxy,or the residue of an amino acid. The term acyl specifically includes butis not limited to acetyl, propionyl, butyryl, pentanoyl,3-methylbutyryl, hydrogen succinate, 3-chlorobenzoate, benzoyl, acetyl,pivaloyl, mesylate, propionyl, valeryl, caproic, caprylic, capric,lauric, myristic, palmitic, stearic, and oleic.

As used herein, the term purine or pyrimidine base, includes, but is notlimited to, 6-alkylpurine and N⁶-alkylpurines, N⁶-acylpurines,N⁶-benzylpurine, 6-halopurine, N⁶-vinylpurine, N⁶-acetylenic purine,N⁶-acyl purine, N⁶-hydroxyalkyl purine, N⁶-thioalkyl purine,N²-alkylpurines, N⁴-alkylpyrimidines, N⁴-acylpyrimidines,4-benzylpyrimidine, N⁴-halopyrimidines, N⁴-acetylenic pyrimidines,4-acyl and N⁴-acyl pyrimidines, 4-hydroxyalkyl pyrimidines, 4-thioalkylpyrimidines, thymine, cytosine, 6-azapyrimidine, including6-azacytosine, 2- and/or 4-mercaptopyrimidine, uracil,C⁵-alkylpyrimidines, C⁵-benzylpyrimidines, C⁵-halopyrimidines,C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine,C⁵-hydroxyalkyl purine, C⁵-amidopyrimidine, C⁵-cyanopyrimidine,C⁵-nitropyrimidine, C⁵-aminopyrimidine, N²-alkylpurines,N²-alkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl,triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, andpyrazolopyrimidinyl. Functional oxygen and nitrogen groups on the basecan be protected as necessary or desired. Suitable protecting groups arewell known to those skilled in the art, and include trimethylsilyl,dimethylhexylsilyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl,trityl, alkyl groups, acyl groups such as acetyl and propionyl,methanesulfonyl, and p-toluenesulfonyl.

As used herein, the term amino acid residue includes but is not limitedto the L or D enantiomers (or any mixture thereof, including a racemicmixture) of alanyl, valinyl, leucinyl, isoleucinyl, prolinyl,phenylalaninyl, tryptophanyl, methioninyl, glycinyl, serinyl,threoninyl, cysteinyl, tyrosinyl, asparaginyl, glutaminyl, aspartoyl,glutaoyl, lysinyl, argininyl, and histidinyl. Preferred amino acids arein the L-stereoconfiguration, and a preferred amino acid moiety isL-valinyl.

The term biologically active nucleoside, as used herein, refers to anucleoside which exhibits an EC₅₀ of 15 micromolar or less when testedin 2.2.15 cells transfected with the hepatitis virion.

Preferred bases include cytosine, 5-fluorocytosine, 5-bromocytosine,5-iodocytosine, uracil, 5-fluorouracil, 5-bromouracil, 5-iodouracil,5-methyluracil, thymine, adenine, guanine, inosine, xanthine,2,6-diaminopurine, 6-aminopurine, 6-chloropurine and 2,6-dichloropurine,6-bromopurine, 2,6-dibromopurine, 6-iodopurine, 2,6-di-iodopurine,5-bromovinylcytosine, 5-bromovinyluracil, 5-bromoethenylcytosine,5-bromoethenyluracil, 5-trifluoromethylcytosine,5-trifluoromethyluracil.

The 2′-deoxy-β-L-erythro-pentofuranonucleoside can be provided as a 5′phospholipid or a 5′-ether lipid, as disclosed in the followingreferences, which are incorporated by reference herein: Kucera, L. S.,N. Lyer, E. Leake, A. Raben, Modest E. J., D. L. W., and C. Piantadosi.1990. Novel membrane-interactive ether lipid analogs that inhibitinfectious HIV-1 production and induce defective virus formation. AIDSRes Hum Retroviruses. 6:491-501; Piantadosi, C., J. Marasco C. J., S. L.morris-Natschke, K. L. Meyer, F. Gumus, J. R. Surles, K. S. Ishaq, L. S.Kucera, N. Iyer, C. A. Wallen, S. Piantadosi, and E. J. Modest.1991-Synthesis and evaluation of novel ether lipid nucleoside conjugatesfor anti-HIV activity. J Med. Chem. 34:1408-1414; Hostetler, K. Y., D.D. Richman, D. A. Carson, L. M. Stuhmiller, G. M. T. van Wijk, and H.van den Bosch. 1992. Greatly enhanced inhibition of humanimmunodeficiency virus type 1 replication in CEM and HT4-6C cells by31-deoxythymidine diphosphate dimyristoylglycerol, a lipid prodrug of31-deoxythymidine. Antimicrob Agents Chemother. 36:2025-2029; Hostetler,K. Y., L. M. Stuhmiller, H. B. Lenting, H. van den Bosch, and D. D.Richman. 1990. Synthesis and antiretroviral activity of phospholipidanalogs of azidothymidine and other antiviral nucleosides. J. Biol.Chem. 265:6112-7.

The 2′-deoxy-β-L-erythro-pentofuranonucleoside can be converted into apharmaceutically acceptable ester by reaction with an appropriateesterifying agent, for example, an acid halide or anhydride. Thenucleoside or its pharmaceutically acceptable prodrug can be convertedinto a pharmaceutically acceptable salt thereof in a conventionalmanner, for example, by treatment with an appropriate base or acid. Theester or salt can be converted into the parent nucleoside, for example,by hydrolysis.

As used herein, the term pharmaceutically acceptable salts or complexesrefers to salts or complexes of the2′-deoxy-β-L-erythro-pentofuranonucleosides that retain the desiredbiological activity of the parent compound and exhibit minimal, if any,undesired toxicological effects. Nonlimiting examples of such salts are(a) acid addition salts formed with inorganic acids (for example,hydrochloric acid, hydrobromic acid, sulfuric acid, phosphoric acid,nitric acid, and the like), and salts formed with organic acids such asacetic acid, oxalic acid, tartaric acid, succinic acid, malic acid,ascorbic acid, benzoic acid, tannic acid, palmoic acid, alginic acid,polyglutamic acid, naphthalenesulfonic acids, naphthalenedisulfonicacids, and polygalacturonic acid; (b) base addition salts formed withcations such as sodium, potassium, zinc, calcium, bismuth, barium,magnesium, aluminum, copper, cobalt, nickel, cadmium, sodium, potassium,and the like, or with an organic cation formed fromN,N-dibenzylethylene-diamine, ammonium, or ethylenediamine; or (c)combinations of (a) and (b); e.g., a zinc tannate salt or the like.

The term prodrug, as used herein, refers to a compound that is convertedinto the nucleoside on administration in vivo. Nonlimiting examples arepharmaceutically acceptable salts (alternatively referred to as“physiologically acceptable salts”), the 5′ and N⁴ or N⁶ acylated oralkylated derivatives of the active compound, and the 5′-phospholipidand 5′-ether lipid derivatives of the active compound.

Modifications of the active compounds, specifically at the N⁴, N⁶ and5′-O positions, can affect the bioavailability and rate of metabolism ofthe active species, thus providing control over the delivery of theactive species. A preferred modification is a 5′-aminoacid ester,including the L-valinyl ester.

A preferred embodiment of the present invention is a method for thetreatment of HBV infections in humans or other host animals, thatincludes administering an effective amount of one or more of a2′-deoxy-β-L-erythro-pentofuranonucleoside derivative selected from thegroup consisting of β-L-2′-deoxyadenosine, β-L-2′-deoxycytidine,β-L-2′-deoxyuridine, β-L-2′-guanosine, β-L-2′-deoxyinosine, andβ-L-2′-deoxythymidine, or a physiologically acceptable prodrug thereof,including a phosphate, 5′ and or N⁶ alkylated or acylated derivative, ora physiologically acceptable salt thereof, optionally in apharmaceutically acceptable carrier. The compounds of this inventioneither possess anti-HBV activity, or are metabolized to a compound orcompounds that exhibit anti-HBV activity. In a preferred embodiment, the2′-deoxy-β-L-erythro-pentofuranonucleoside is administered substantiallyin the form of a single isomer, i.e., at least approximately 95% in thedesignated stereoconfiguration.

Nucleotide Prodrugs

Any of the nucleosides described herein can be administered as astabilized nucleotide prodrug to increase the activity, bioavailability,stability or otherwise alter the properties of the nucleoside. A numberof nucleotide prodrug ligands are known. In general, alkylation,acylation or other lipophilic modification of the mono, di ortriphosphate of the nucleoside will increase the stability of thenucleotide. Examples of substituent groups that can replace one or morehydrogens on the phosphate moiety are alkyl, aryl, steroids,carbohydrates, including sugars, 1,2-diacylglycerol and alcohols. Manyare described in R. Jones and N. Bischofberger, Antiviral Research, 27(1995) 1-17. Any of these can be used in combination with the disclosednucleosides to achieve a desired effect.

In one embodiment, the 2′-deoxy-β-L-erythro-pentofuranonucleoside isprovided as 5′-hydroxyl lipophilic prodrug. Nonlimiting examples of U.S.patents that disclose suitable lipophilic substituents that can becovalently incorporated into the nucleoside, preferably at the 5′-OHposition of the nucleoside or lipophilic preparations, include U.S. Pat.No. 5,149,794 (Sep. 22, 1992, Yatvin et al.); U.S. Pat. No. 5,194,654(Mar. 16, 1993, Hostetler et al., U.S. Pat. No. 5,223,263 (Jun. 29,1993, Hostetler et al.); U.S. Pat. No. 5,256,641 (Oct. 26, 1993, Yatvinet al.); U.S. Pat. No. 5,411,947 (May 2, 1995, Hostetler et al.); U.S.Pat. No. 5,463,092 (Oct. 31, 1995, Hostetler et al.); U.S. Pat. No.5,543,389 (Aug. 6, 1996, Yatvin et al.); U.S. Pat. No. 5,543,390 (Aug.6, 1996, Yatvin et al.); U.S. Pat. No. 5,543,391 (Aug. 6, 1996, Yatvinet al.); and U.S. Pat. No. 5,554,728 (Sep. 10, 1996; Basava et al.), allof which are incorporated herein by reference.

Foreign patent applications that disclose lipophilic substituents thatcan be attached to the 2′-deoxy-β-L-erythro-pentofuranonucleosidederivative of the present invention, or lipophilic preparations, includeWO 89/02733, WO 90/00555, WO 91/16920, WO 91/18914, WO 93/00910, WO94/26273, WO 96/15132, EP 0 350 287, EP 93917054.4, and WO 91/19721.

Additional nonlimiting examples of2′-deoxy-β-L-erythro-pentofuranonucleosides are those that containsubstituents as described in the following publications. Thesederivatized 2′-deoxy-β-L-erythro-pentofuranonucleosides can be used forthe indications described in the text or otherwise as antiviral agents,including as anti-HBV agents. Ho, D. H. W. (1973) Distribution of kinaseand deaminase of 1 β-D-arabinofuranosylcytosine in tissues of man andmouse. Cancer Res. 33, 2816-2820; Holy, A. (1993) Isopolarphosphorous-modified nucleotide analogues. In: De Clercq (Ed.), Advancesin Antiviral Drug Design, Vol. I, JAI Press, pp. 179-231; Hong, C. I.,Nechaev, A., and West, C. R. (1979a) Synthesis and antitumor activity of1□-D-arabinofuranosylcytosine conjugates of cortisol and cortisone.Biochem. Biophys. Rs. Commun. 88, 1223-1229; Hong, C. I., Nechaev, A.,Kirisits, A. J. Buchheit, D. J. and West, C. R. (1980) Nucleosideconjugates as potential antitumor agents. 3. Synthesis and antitumoractivity of 1-(β-D-arabinofuranosyl) cytosine conjugates ofcorticosteriods and selected lipophilic alcohols. J. Med. Chem. 28,171-177; Hostetler, K. Y., Stuhmiller, L. M., Lenting, H. B. M. van denBosch, H. and Richman, D. D. (1990) Synthesis and antiretroviralactivity of phospholipid analogs of azidothymidine and other antiviralnucleosides. J. Biol. Chem. 265, 6112-6117; Hostetler, K. Y., Carson, D.A. and Richman, D. D. (1991); Phosphatidylazidothymidine: mechanism ofantiretroviral action in CEM cells. J. Biol. Chem. 266, 11714-11717;Hostetler, K. Y., Korba, B. Sridhar, C., Gardener, M. (1994a) Antiviralactivity of phosphatidyl-dideoxycytidine in hepatitis B-infected cellsand enhanced hepatic uptake in mice. Antiviral Res. 24, 59-67;Hostetler, K. Y., Richman, D. D., Sridhar, C. N. Felgner, P. L, Felgner,J., Ricci, J., Gardener, M. F. Selleseth, D. W. and Ellis, M. N. (1994b)Phosphatidylazidothymidine and phosphatidyl-ddC: Assessment of uptake inmouse lymphoid tissues and antiviral activities in humanimmunodeficiency virus-infected cells and in rauscher leukemiavirus-infected mice. Antimicrobial Agents Chemother. 38, 2792-2797;Hunston, R. N., Jones, A. A. McGuigan, C., Walker, R. T., Balzarini, J.,and De Clercq, E. (1984) Synthesis and biological properties of somecyclic phosphotriesters derived from 2′-deoxy-5-fluorouridine. J. Med.Chem. 27, 440-444; Ji, Y. H., Moog, C., Schmitt, G., Bischoff, P. andLuu, B. (1990); Monophosphoric acid diesters of 7β-hydroxycholesteroland of pyrimidine nucleosides as potential antitumor agents: synthesisand preliminary evaluation of antitumor activity. J. Med. Chem. 33,2264-2270; Jones, A. S., McGuigan, C., Walker, R. T., Balzarini, J. andDeClercq, E. (1984) Synthesis, properties, and biological activity ofsome nucleoside cyclic phosphoramidates. J. Chem. Soc. Perkin Trans. 1,1471-1474; Juodka, B. A. and Smart, J. 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(1990c) Synthesis of some novel dialkyl phosphatederivative of 3′-modified nucleosides as potential anti-AIDS drugs.Antiviral Chem. Chemother. 1, 25-33; McGuigan, C., Devine, K. G.,O'Connor, T. J., and Kinchington, D. (1991) Synthesis and anti-HIVactivity of some haloalkyl phosphoramidate derivatives of3′-azido-3′-deoxythymidine (AZT); potent activity of the trichloroethylmethoxyalaninyl compound. Antiviral Res. 15, 255-263; McGuigan, C.,Pathirana, R. N., Mahmood, N., Devine, K. G. and Hay, A. J. (1992) Arylphosphate derivatives of AZT retain activity against HIV-1 in cell lineswhich are resistant to the action of AZT. Antiviral Res. 17, 311-321;McGuigan, C., Pathirana, R. N., Choi, S. M., Kinchington, D. andO'Connor, T. J. (1993a) Phosphoramidate derivatives of AZT as inhibitorsof HIV; studies on the carboxyl terminus. Antiviral Chem. Chemother. 4,97-101; McGuigan, C., Pathirana, R. N., Balzarini, J. and De Clercq, E.(1993b) Intracellular delivery of bioactive AZT nucleotides by arylphosphate derivatives of AZT. J. Med. Chem. 36, 1048-1052.

The question of chair-twist equilibria for the phosphate rings ofnucleoside cyclic 3′,5′-monophosphates. ¹HNMR and x-ray crystallographicstudy of the diasteromers of thymidine phenyl cyclic3′,5′-monophosphate. J. Am. Chem. Soc. 109, 4058-4064; Nerbonne, J. M.,Richard, S., Nargeot, J. and Lester, H. A. (1984) New photoactivatablecyclic nucleotides produce intracellular jumps in cyclic AMP and cyclicGMP concentrations. Nature 301, 74-76; Neumann, J. M., Hervé, M.,Debouzy, J. C., Guerra, F. I., Gouyette, C., Dupraz, B. and Huynh-Dinh,T. (1989) Synthesis and transmembrane transport studies by NMR of aglucosyl phospholipid of thymidine. J. Am. Chem. Soc. 111, 4270-4277;Ohno, R., Tatsumi, N., Hirano, M., Imai, K. Mizoguchi, H., Nakamura, T.,Kosaka, M., Takatuski, K., Yamaya, T., Toyama, K., Yoshida, T., Masaoka,T., Hashimoto, S., Ohshima, T., Kimura, I., Yamada, K. and Kimura, J.(1991) Treatment of myelodysplastic syndromes with orally administered1-β-D-rabinofuranosylcytosine-5′-stearylphosphate. Oncology 48, 451-455.

Palomino, E., Kessle, D. and Horwitz, J. P. (1989) A dihydropyridinecarrier system for sustained delivery of 2′,3′-dideoxynucleosides to thebrain. J. Med. Chem. 32, 622-625; Perkins, R. M., Barney, S., Wittrock,R., Clark, P. H., Levin, R. Lambert, D. M., Petteway, S. R.,Serafinowska, H. T., Bailey, S. M., Jackson, S., Harmden, M. R. Ashton,R., Sutton, D., Harvey, J. J. and Brown, A. G. (1993) Activity ofBRL47923 and its oral prodrug, SB203657A against a rauscher murineleukemia virus infection in mice. Antiviral Res. 20 (Suppl. I). 84;Piantadosi, C., Marasco, C. J., Jr., Morris-Natschke, S. L., Meyer, K.L., Gumus, F., Surles, J. R., Ishaq, K. S., Kucera, L. S. Iyer, N.,Wallen, C. A., Piantadosi, S, and Modest, E. J. (1991) Synthesis andevaluation of novel ether lipid nucleoside conjugates for anti-HIV-1activity. J. Med. Chem. 34, 1408-1414; Pompon, A., Lefebvre, I., Imbach,J. L., Kahn, S, and Farquhar, D. (1994) Decomposition pathways of themono- and bis(pivaloyloxymethyl) esters ofazidothymidine-5′-monophosphate in cell extract and in tissue culturemedium; an application of the ‘on-line ISRP-cleaning’ HPLC technique.Antiviral Chem. Chemother. 5, 91-98; Postemark, T. (1974) Cyclic AMP andcyclic GMP. Annu. Rev. Pharmacol. 14, 23-33; Prisbe, E. J., Martin, J.C. M., McGee, D. P. C., Barker, M. F., Smee, D. F. Duke, A. E.,Matthews, T. R. and Verheyden, J. P. J. (1986) Synthesis and antiherpesvirus activity of phosphate and phosphonate derivatives of9-[(1,3-dihydroxy-2-propoxy) methyl]guanine. J. Med. Chem. 29, 671-675;Puech, F., Gosselin, G., Lefebvre, I., Pompon, A., Aubertin, A. M. Dirn,A. and Imbach, J. L. (1993) Intracellular delivery of nucleosidemonophosphate through a reductase-mediated activation process. AntiviralRes. 22, 155-174; Pugaeva, V. P., Klochkeva, S. I., Mashbits, F. D. andEizengart, R. S. (1969). Robins, R. K. (1984) The potential ofnucleotide analogs as inhibitors of retroviruses and tumors. Pharm. Res.11-18; Rosowsky, A., Kim. S. H., Ross and J. Wick, M. M. (1982)Lipophilic 5′-(alkylphosphate) esters of 1-β-D-arabinofuranosylcytosineand its N⁴-acyl and 2.2′-anhydro-3′-O-acyl derivatives as potentialprodrugs. J. Med. Chem. 25, 171-178; Ross, W. (1961) Increasedsensitivity of the walker turnout towards aromatic nitrogen mustardscarrying basic side chains following glucose pretreatment. Biochem.Pharm. 8, 235-240; Ryu, E. K., Ross, R. J. Matsushita, T., MacCoss, M.,Hong, C. I. and West, C. R. (1982). Phospholipid-nucleoside conjugates.3. Synthesis and preliminary biological evaluation of1-β-D-arabinofuranosylcytosine 5′diphosphate[−], 2-diacylglycerols. J.Med. Chem. 25, 1322-1329; Saffhill, R. and Hume, W. J. (1986) Thedegradation of 5-iododeoxyuridine and 5-bromodeoxyuridine by serum fromdifferent sources and its consequences for the use of these compoundsfor incorporation into DNA. Chem. Biol. Interact. 57, 347-355;Saneyoshi, M., Morozumi, M., Kodama, K., Machida, J., Kuninaka, A. andYoshino, H. (1980) Synthetic nucleosides and nucleotides. XVI. Synthesisand biological evaluations of a series of 1-β-D-arabinofuranosylcytosine5′-alkyl or arylphosphates. Chem. Pharm. Bull. 28, 2915-2923; Sastry, J.K., Nehete, P. N., Khan, S., Nowak, B. J., Plunkett, W., Arlinghaus, R.B. and Farquhar, D. (1992) Membrane-permeable dideoxyuridine5′-monophosphate analogue inhibits human immunodeficiency virusinfection. Mol. Pharmacol. 41, 441-445; Shaw, J. P., Jones, R. J.Arimilli, M. N., Louie, M. S., Lee, W. A. and Cundy, K. C. (1994) Oralbioavailability of PMEA from PMEA prodrugs in mate Sprague-Dawley rats.9th Annual AAPS Meeting. San Diego, Calif. (Abstract). Shuto, S., Ueda,S., Imamura, S., Fukukawa, K. Matsuda, A. and Ueda, T. (1987) A facileone-step synthesis of 5′-phosphatidylnucleosides by an enzymatictwo-phase reaction. Tetrahedron Lett. 28, 199-202; Shuto, S., Itoh, H.,Ueda, S., Imamura, S., Kukukawa, K., Tsujino, M., Matsuda, A. and Ueda,T. (1988) A facile enzymatic synthesis of5′-(3-sn-phosphatidyl)nucleosides and their antileukemic activities.Chem. Pharm. Bull. 36, 209-217. One preferred phosphate prodrug group isthe S-acyl-2-thioethyl group, also referred to as “SATE.”

Combination or Alternation Therapy

It has been recognized that drug-resistant variants of HBV can emergeafter prolonged treatment with an antiviral agent. Drug resistance mosttypically occurs by mutation of a gene that encodes for an enzyme usedin the viral life cycle, and most typically in the case of HBV, DNApolymerase. Recently, it has been demonstrated that the efficacy of adrug against HBV infection can be prolonged, augmented, or restored byadministering the compound in combination or alternation with a second,and perhaps third, antiviral compound that induces a different mutationfrom that caused by the principle drug. Alternatively, thepharmacokinetics, biodistribution, or other parameter of the drug can bealtered by such combination or alternation therapy. In general,combination therapy is typically preferred over alternation therapybecause it induces multiple simultaneous stresses on the virus.

The anti-hepatitis B viral activity of β-L-2′-dA, β-L-2′-dC, β-L-2′-dU,β-L-2′-dG, β-L-2′-dT, β-L-dI, or other β-L-2′-nucleosides providedherein, or the prodrugs, phosphates, or salts of these compounds, can beenhanced by administering two or more of these nucleosides incombination or alternation. Alternatively, for example, one or more ofβ-L-2′-dA, β-L-2′-dC, β-L-2′-dU, β-L-2′-dG, β-L-2′-dT, β-L-dI, or otherβ-L-2′-nucleosides provided herein can be administered in combination oralternation with 3TC, FTC, L-FMAU, DAPD, famciclovir, penciclovir,BMS-200475, bis pom PMEA (adefovir, dipivoxil); lobucavir, ganciclovir,or ribavarin.

In any of the embodiments described herein, if the β-L-2′-nucleoside ofthe present invention is administered in combination or alternation witha second nucleoside or nonnucleoside reverse transcriptase inhibitorthat is phosphorylated to an active form, it is preferred that a secondcompound be phosphorylated by an enzyme that is different from thatwhich phosphorylates the selected β-L-2′-nucleoside of the presentinvention in vivo. Examples of kinase enzymes are thymidine kinase,cytosine kinase, guanosine kinase, adenosine kinase, deoxycytidinekinase, 5′-nucleotidase, and deoxyguanosine kinase.

Preparation of the Active Compounds

The 2′-deoxy-β-L-erythro-pentofuranonucleoside derivatives of thepresent invention are known in the art and can be prepared according tothe method disclosed by Holy, Collect. Czech. Chem. Commun. (1972),37(12), 4072-87 and Mol. Phys. (1967), 3(4), 386-95.

A general process for obtaining β-L-erythro-pentafuranonucleosides(β-L-dN) is shown in FIG. 1, using L-ribose or L-xylose as a startingmaterial.

Mono, di, and triphosphate derivatives of the active nucleosides can beprepared as described according to published methods. The monophosphatecan be prepared according to the procedure of Imai et al., J. Org.Chem., 34(6), 1547-1550 (June 1969). The diphosphate can be preparedaccording to the procedure of Davisson et al., J. Org. Chem., 52(9),1794-1801 (1987). The triphosphate can be prepared according to theprocedure of Hoard et al., J. Am. Chem. Soc., 87(8), 1785-1788 (1965).

Experimental Protocols

Melting points were determined in open capillary tubes on a GallenkampMFB-595-010 M apparatus and are uncorrected. The UV absorption spectrawere recorded on an Uvikon 931 (KONTRON) spectrophotometer in ethanol.¹H-NMR spectra were run at room temperature in DMSO-d₆ with a Bruker AC250 or 400 spectrometer. Chemical shifts are given in ppm, DMSO-d₅ beingset at 2.49 ppm as reference. Deuterium exchange, decoupling experimentsor 2D-COSY were performed in order to confirm proton assignments. Signalmultiplicities are represented by s (singlet), d (doublet), dd (doubletof doublets), t (triplet), q (quadruplet), br (broad), m (multiplet).All J-values are in Hz. FAB mass spectra were recorded in thepositive-(FAB>0) or negative-(FAB<0) ion mode on a JEOL DX 300 massspectrometer The matrix was 3-nitrobenzyl alcohol (NBA) or a mixture(50:50, v/v) of glycerol and thioglycerol (GT). Specific rotations weremeasured on a Perkin-Elmer 241 spectropolarimeter (path length 1 cm) andare given in units of 10⁻¹ deg cm² g⁻¹. Elemental analysis were carriedout by the “Service de Microanalyses du CNRS, Division de Vernaison”(France). Analyses indicated by the symbols of the elements or functionswere within ±0.4% of theoretical values. Thin layer chromatography wasperformed on precoated aluminium sheets of Silica Gel 60 F₂₅₄ (Merck,Art. 5554), visualisation of products being accomplished by UVabsorbency followed by charring with 10% ethanolic sulfuric acid andheating. Column chromatography was carried out on Silica Gel 60 (Merck,Art. 9385) at atmospheric pressure.

EXAMPLE 1 Stereospecific Synthesis of 2′-Deoxy-β-L-Adenosine

9-(3,5-Di-O-benzoyl-β-L-xylofuranosyl)adenine (3)

A solution of 9-(2-O-acetyl-3,5-di-O-benzoyl-β-L-xylofuranosyl)adenine 2[Ref.: Gosselin, G.; Bergogne, M.-C.; Imbach, J.-L., “Synthesis andAntiviral Evaluation of β-L-Xylofuranosyl Nucleosides of the FiveNaturally Occurring Nucleic Acid Bases”, Journal of HeterocyclicChemistry, 1993, 30 (October-November), 1229-1233] (8.30 g, 16.05 mmol)and hydrazine hydrate 98% (234 mL, 48.5 mmol) in a mixture ofpyridine/glacial acetic acid (4/1, v/v, 170 mL) was stirred at roomtemperature for 22 h. The reaction was quenched by adding acetone (40mL) and stirring was continued for one additional hour. The reactionmixture was reduced to one half of its volume, diluted with water (250mL) and extracted with chloroform (2×150 mL). The organic layer waswashed successively with an aqueous saturated solution of NaHCO₃ (3×100mL) and water (3×100 mL), dried, filtered, concentrated andco-evaporated with toluene and methanol. The residue was purified bysilica gel column chromatography (0-3% MeOH in dichloromethane) to give3 (5.2 g, 68%) precipitated from diisopropylic ether: ¹H NMR (DMSO-d₆):δ 4.5-4.9 (m, 4H, H-2′, H-4′, H-5′ and H-5″), 5.64 (t, 1H, H-3′,J_(2′,3′)=J_(3′,4′)=3.5 Hz), 6.3 (br s, 1H, OH-2′), 6.45 (d, 1H, H-1′,J_(1′,2′)=4.6 Hz), 7.3 (br s, 2H, NH₂-6), 7.4-7.9 (m, 10H, 2 benzoyls),8.07 and 8.34 (2s, 2H, H-2 and H-8); ms: matrix G/T, (FAB⁺) m/z 476[M+H]⁺, 136 [BH₂]⁺, (FAB⁻) m/z 474 [M−H]⁻, 134 [B]⁻; UV (95% ethanol):λ_(max) 257 nm (ε 16400), 230 μm (ε 29300), λ_(min) 246 nm (ε 14800);[α]_(D) ²⁰=−64 (c 1.07, CHCl₃). Anal. Calcd for C₂₄H₂₁N₅O₄ (M=475.45):C, 60.43; H, 4.45; N, 14.73. Found: C, 60.41; H, 4.68; N, 14.27.

9-(3,5-Di-O-benzoyl-2-deoxy-β-L-threo-pentofuranosyl)adenine (4).

To a solution of compound 3 (1.00 g, 2.11 mmol) in dry acetonitrile (65mL) were added 4-(dimethylamino)pyridine (0.77 g, 6.32 mmol) andphenoxythiocarbonyl chloride (0.44 mL, 3.16 mmol). The mixture wasstirred at room temperature for 2 h. After concentration, the residuewas dissolved in dichloromethane (50 mL) and washed successively withwater (2×30 mL), aqueous solution of hydrochloric acid 0.5 N (30 mL) andwater (3×30 mL). The organic layer was dried, filtered and concentratedto dryness. The crude thiocarbonylated intermediate was directly treatedwith tris-(trimethylsilyl)silane hydride (0.78 mL, 5.23 mmol) andα,α′-azoisobutyronitrile (AIBN, 0.112 g, 0.69 mmol) in dry dioxane (17mL) at reflux for 2 h. The solvent was removed under vacuum and theresidue was purified by silica gel column chromatography (0-5% MeOH indichloromethane) to give pure 4 (0.93 g, 96%) as a foam: ¹H NMR(DMSO-d₆): δ 2.9-3.1 (m, 2H, H-2′ and H-2″), 4.6-4.7 (m, 3H, H-4′, H-5′and H-5″), 5.8 (br s, 1H, H-3′), 6.43 (dd, 1H, H-1′, J_(1′,2′)=3.1 Hz,J_(1′,2″)=7.6 Hz), 7.3 (br s, 2H, NH₂-6), 7.4-7.9 (m, 10H, 2 benzoyls),8.05 and 8.33 (2s, 2H, H-2 and H-8); ms: matrix G/T, (FAB⁺) m/z 460[M+H]⁺, 325 [S]⁺, 136 [BH₂]⁺, (FAB⁻) m/z 458 [M−H]⁻, 134 [B]⁻; UV (95%ethanol): λ_(max) 261 nm (ε 14400), 231 nm (ε 26300), λ_(min) 249 nm (ε12000); [α]_(D) ²⁰=−38 (c 1.04, DMSO).

6-N-(4-Monomethoxytrityl)-9-(3,5-di-O-benzoyl-2-deoxy-β-L-threo-pentofuranosyl)adenine(5).

To a solution of compound 4 (0.88 g, 1.92 mmol) in dry pyridine (40 mL)was added 4-monomethoxytrityl chloride (1.18 g, 3.84 mmol). The mixturewas stirred at 60° C. for 24 h. After addition of methanol (5 mL), thesolution was concentrated to dryness, the residue was dissolved indichloromethane (50 mL) and washed successively with water (30 mL),aqueous saturated NaHCO₃ (30 mL) and water (30 mL). The organic layerwas dried, filtered, concentrated and co-evaporated with toluene to givepure 5 (1.01 g, 72%) as a foam: ¹H NMR (CDCl₃): δ 2.9-3.0 (m, 2H, H-2′and H-2″), 3.62 (s, 3H, OCH₃), 4.6-4.8 (m, 3H, H-4′, H-5′ and H-5″),5.85 (pt, 1H, H-3′), 6.44 (dd, 1H, H-1′, J_(1′,2′)=3.1 Hz, J_(1′,2″)=7.3Hz), 6.9 (br s, 1H, NH-6), 6.7-6.8 and 7.2-7.4 (2m, 24H, 2 benzoyls andMMTr), 7.97 and 8.13 (2s, 2H, H-2 and H-8); ms: matrix G/T, (FAB⁺) m/z732 [M+H]⁺, (FAB⁻) m/z 730 [M−H]⁻; UV (95% ethanol): λ_(max) 274 nm (ε12100), 225 nm (ε 24200), λ_(min) 250 nm (ε 5900); [α]_(D) ²⁰=−16 (c1.12, DMSO).

6-N-(4-Monomethoxytrityl)-9-(2-deoxy-β-L-threo-pentofuranosyl)-adenine(6).

Compound 5 (0.95 g, 1.30 mmol) was treated with a solution (saturated at−10° C.) of methanolic ammonia (40 mL), at room temperature overnight.After concentration, the residue was dissolved in dichloromethane (60mL) and washed with water (30 mL). The aqueous layer was extracted twicewith dichloromethane (10 mL). The combined organic layer was dried,filtered and concentrated. The residue was purified by silica gel columnchromatography (0-5% MeOH in dichloromethane) to give pure 6 (0.67 g,98%) as a foam: ¹H NMR (CDCl₃): δ 2.6-2.9 (m, 2H, H-2′ and H-2″), 3.5(br s, 1H, OH-5′), 3.55 (s, 3H, OCH₃), 3.9-4.0 (m, 3H, H-4′, H-5′ andH-5″), 4.5-4.6 (m, 1H, H-3′), 6.03 (dd, 1H, H-1′, J_(1′,2′)=4.0 Hz,J_(1′,2″)=8.8 Hz), 7.0 (br s, 1H, NH-6), 6.7-6.8 and 7.1-7.4 (2m, 14H,MMTr), 7.40 (d, 1H, OH-3′, J_(H,OH)=10.6-Hz), 7.80 and 7.99 (2s, 2H, H-2and H-8); ms: matrix G/T, (FAB⁺) m/z 524 [M+H]⁺, 408 [BH₂]⁺, (FAB⁻) m/z1045 [2M−H]⁻, 522 [M−H]⁻, 406 [B]⁻; UV (95% ethanol): λ_(max) 275 nm (ε12300), λ_(min) 247 nm (ε 3600); [α]_(D) ²⁰=+28 (c 0.94, DMSO).

6-N-(4-Monomethoxytrityl)-9-(2-deoxy-5-O-(4-monomethoxytrityl)-β-L-threo-pentofuranosyl)adenine(7).

Compound 6 (0.62 g, 1.24 mmol) in dry pyridine (25 mL) was treated with4-monomethoxytrityl chloride (0.46 g, 1.49 mmol) at room temperature for16 h. After addition of methanol (5 mL), the mixture was concentrated todryness. The residue was dissolved in dichloromethane (60 mL) and washedsuccessively with water (40 mL), a saturated aqueous solution of NaHCO₃(40 mL) and water (3×40 mL). The organic layer was dried, filtered,concentrated and co-evaporated with toluene and methanol. The residuewas purified by silica gel column chromatography (0-10% MeOH indichloromethane) to give 7 (0.71 g, 72%) as a foam: ¹H NMR (DMSO-d₆): δ2.21 (d, 1H, H-2′ J_(2′,2″)=14.3 Hz), 2.6-2.7 (m, 1H, H-2″), 3.1-3.3(2m, 2H, H-5′ and H-5″), 3.64 and 3.65 (2s, 6H, 2×OCH₃), 4.1-4.2 (m, 1H,H-4′), 4.2-4.3 (m, 1H, H-3′), 5.68 (d, 1H, OH-3′, J_(H,OH)=5.2 Hz), 6.24(d, 1H, H-1′, J_(1′,2″)=7.0 Hz), 6.7-6.8 and 7.1-7.3 (2m, 29H, 2 MMTrand NH-6), 7.83 and 8.21 (2s, 2H, H-2 and H-8); ms: matrix G/T, (FAB⁺)m/z 796 [M+H]⁺, 408 [BH₂]⁺, (FAB⁻) m/z 794 [M−H]⁻, 406 [B]⁻; UV (95%ethanol): λ_(max) 275 nm (ε 30900), λ_(min) 246 nm (ε 12800); [α]_(D)²⁰=+14 (c 1.03, DMSO).

6-N-(4-Monomethoxytrityl)-9-(3-O-benzoyl-2-deoxy-5-O-(4-mono-methoxytrityl)-β-L-erythro-pentofuranosyl)adenine (8).

A solution of diethylazodicarboxylate (0.38 mL, 2.49 mmol) in drytetrahydrofuran (20 mL) was added dropwise to a cooled solution (0° C.)of nucleoside 7 (0.66 g, 0.83 mmol), triphenylphosphine (0.66 g, 2.49mmol) and benzoic acid (0.30 g, 2.49 mmol) in dry THF (20 mL). Themixture was stirred at room temperature for 18 h and methanol (1 mL) wasadded. The solvents were removed under reduced pressure and the crudematerial was purified by silica gel column chromatography (0-5% ethylacetate in dichloromethane) to give compound 8 slightly contaminated bytriphenylphosphine oxide.

6-N-(4-Monomethoxytrityl)-9-(2-deoxy-5-O-(4-monomethoxytrityl)-β-L-erythro-pentofuranosyl)adenine(9).

Compound 8 was treated by a solution (saturated at −10° C.) ofmethanolic ammonia (20 mL), at room temperature for 24 h, then thereaction mixture was concentrated to dryness. The residue was dissolvedin dichloromethane (30 mL) and washed with water (20 mL). The aqueouslayer was extracted by dichloromethane (2×20 mL) and the combinedorganic phase was dried, filtered and concentrated. Pure compound 9(0.50 g, 76% from 7) was obtained as a foam after purification by silicagel column chromatography (0-2% MeOH in dichloromethane): ¹H NMR(DMSO-d₆): δ 2.2-2.3 (m, 1H, H-2′), 2.8-2.9 (m, 1H, H-2″), 3.1-3.2 (m,2H, H-5′ and H-5″), 3.64 and 3.65 (2s, 6H, 2×OCH₃), 3.97 (pq, 1H, H-4′),4.4-4.5 (m, 1H, H-3′), 5.36 (d, 1H, OH-3′, J_(H,OH)=4.5 Hz), 6.34 (t,1H, H-1′, J_(1′,2′)=J_(1′,2″)=6.4 Hz), 6.8-6.9 and 7.1-7.4 (2m, 29H, 2MMTr and NH-6), 7.81 and 8.32 (2s, 2H, H-2 and H-8); ms: matrix G/T,(FAB⁺) m/z 796 [M+H]⁺, 408 [BH₂]⁺, (FAB⁻) m/z 794 [M−H]⁻, 406 [B]⁻; UV(95% ethanol): λ_(max) 276 nm (ε 42600), λ_(min) 248 nm (ε 23300);[α]_(D) ²⁰=+29 (c 1.05, DMSO).

2′-Deoxy-β-L-adenosine (β-L-dA)

Compound 9 (0.44 g, 0.56 mmol) was treated with an aqueous solution ofacetic acid 80% (17 mL) at room temperature for 5 h. The mixture wasconcentrated to dryness, the residue was dissolved in water (20 mL) andwashed with diethyl ether (2×15 mL). The aqueous layer was concentratedand co-evaporated with toluene and methanol. The desired2′-deoxy-β-L-adenosine (β-L-dA) (0.12 g, 83%) was obtained afterpurification by silica gel column chromatography (0-12% MeOH indichloromethane) and filtration through a Millex HV-4 unit (0.45 μ,Millipore): mp 193-194° C. (crystallized from water) (Lit. 184-185° C.for L-enantiomer [Ref.: Robins, M. J.; Khwaja, T. A.; Robins, R. K. J.Org. Chem. 1970, 35, 636-639] and 187-189° C. for D-enantiomer [Ref.:Ness, R. K. in Synthetic Procedures in Nucleic Acid Chemistry; Zorbach,W. W., Tipson, R. S., Eds.; J. Wiley and sons: New York, 1968; Vol 1, pp183-187]; ¹H NMR (DMSO-d₆): δ 2.2-2.3 and 2.6-2.7 (2m, 2H, H-2′ andH-2″), 3.4-3.6 (2m, 2H, H-5′ and H-5″), 3.86 (pq, 1H, H-4′), 4.3-4.4 (m,1H, H-3′), 5.24 (t, 1H, OH-5′, J_(H,OH)=5.8 Hz), 5.30 (d, 1H, OH-3′,J_(H,OH)=4.0 Hz), 6.32 (dd, 1H, H-1′, J_(1′,2′)=6.2 Hz, J_(1′,2″)=7.8Hz), 7.3 (br s, 2H, NH₂-6), 8.11 and 8.32 (2s, 2H, H-2 and H-8); ms:matrix G/T, (FAB⁺) m/z 252 [M+H]⁺, 136 [BH₂]⁺, (FAB⁻) m/z 250 [M−H]⁻,134 [B]⁻; UV (95% ethanol): λ_(max) 258 nm (ε 14300), λ_(min) 226 nm (ε2100); [α]_(D) ²⁰=+25 (c 1.03, H₂O), (Lit. [α]_(D) ²⁰=+23 (c 1.0, H₂O)for L-enantiomer [Ref.: Robins, M. J.; Khwaja, T. A.; Robins, R. K. J.Org. Chem. 1970, 35, 636-639] and [α]_(D) ²⁰=−25 (c 0.47, H₂O) forD-enantiomer [Ref.: Ness, R. K. in Synthetic Procedures in Nucleic AcidChemistry; Zorbach, W. W., Tipson, R. S., Eds.; J. Wiley and sons: NewYork, 1968; Vol 1, pp 183-187]). Anal. Calcd for C₁₀H₁₃N₅O₃+1.5 H₂O(M=278.28): C, 43.16; H, 5.80; N, 25.17. Found: C, 43.63; H, 5.45; N,25.33.

EXAMPLE 2 Stereoselective Synthesis of 2′-Deoxy-β-L-Adenosine (β-L-dA)

Reaction 1:

-   Precursor: L-ribose (Cultor Science Food, CAS [24259-59-4], batch    RIB9711013)-   Reactants: Sulphuric acid 95-97% (Merck; ref 1.00731.1000); Benzoyl    chloride (Fluka; ref 12930); Sodium sulfate (Prolabo; ref 28111.365)-   Solvents: Methanol P.A. (Prolabo; ref 20847.295); Pyridine 99%    (Acros; ref 131780025); Dichloromethane P.A. (Merck; ref    1.06050.6025); Acetic acid P.A. (carlo erba; ref 20104298); Acetic    anhydride (Fluka; ref 45830); Ethanol 95 (Prolabo; ref 20823.293)-   References: Recondo, E. F., and Rinderknecht, H., Eine neue,    Einfache Synthese des 1-O-Acetyl-2,3,5-Tri-O-β-D-Ribofuranosides.    Helv. Chim. Acta, 1171-1173 (1959).

A solution of L-ribose 140 (150 g, 1 mol) in methanol (2 liters) wastreated with sulphuric acid (12 ml) and left at +4° C. for 12 hrs, andthen neutralised with pyridine (180 ml). Evaporation gave an α,β mixtureof methyl ribofuranosides 141 as a syrup. A solution of this anomericmixture in pyridine (1.3 liters) was treated with benzoyl chloride (580ml, 5 mol) with cooling and mechanical stirring. The solution was leftat room temperature for 12 hrs and then poured on ice (about 10 liters)with continued stirring. The mixture (an oil in water) was filtered on aCellite bed. The resulting oil on the cellite bed was washed with water(3×3 liters) and then dissolved with ethyl acetate (3 liters). Theorganic phase was washed with a 5% NaHCO₃ solution (2 liters) and water(2 liters), dried over sodium sulfate, filtered and evaporated to give1-O-methyl-2,3,5-tri-O-benzoyl-α/β-L-ribofuranose 142 as a thick syrup.The oil was dissolved in acetic anhydride (560 ml) and acetic acid (240ml). The solution was, after the dropwise addition of concentratedsulphuric acid (80 ml), kept in the cold (+4° C.) under mechanicalstirring for 10 hrs. The solution was then poured on ice (about 10liters) under continued stirring. The mixture (oily compound in water)was filtered on a Cellite bed. The resulting gummy solid on the cellitebed was washed with water (3×3 liters) and then dissolved indichloromethane (2.5 liters). The organic phase was washed with 5%NaHCO₃ (1 liter) and water (2×2 liters), dried over sodium sulfate,filtered and evaporated to give a gummy solid 143, which wascrystallized from ethanol 95 (yield 225 g, 44%).

Analyses for 1-O-acetyl-2,3,5-tri-O-benzoyl-β-L-ribofuranose 143:

mp 129-130° C. (EtOH 95) (lit. (1) mp 130-131° C.) ¹H NMR (200 MHz,CDCl₃): δ 8.09-7.87 (m, 6H, H_(Arom)), 7.62-7.31 (m, 9H, H_(Arom)) 6.43(s, 1H, H₁), 5.91 (dd, 1H, H₃, J_(3,4) 6.7 Hz; J_(3,2) 4.9 Hz), 5.79(pd, 1H, H₂, J_(2,3) 4.9 Hz; J_(1,2)<1), 4.78 (m, 2H, H₄ and H₅), 4.51(dd, 1H, H₅, J_(5,5′) 13.1 Hz, J_(5′,4) 5.5 Hz), 2.00 (s, 3H, CH₃CO);(identical to commercial1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose) Mass analysis (FAB+,GT) m/z 445 (M-OAc)+ Elemental analysis C₂₈H₂₄O₉ Calculated C, 66.66; H,4.79; found C, H.

Reaction 2:

-   Precursor: Adenine (Pharma-Waldhof; ref 400134.001 lot 45276800)-   Reactants: Stannic chloride fuming (Fluka; ref 96558); NH₃/Methanol    (methanol saturated with NH₃; see page 5); Sodium sulfate (Prolabo;    ref 28111.365)-   Solvents: Acetonitrile (Riedel-de Hean; ref 33019; distilled over    CaH₂); Chloroform Pur (Acros; ref 22706463); Ethyl acetate Pur    (Carlo erba; ref 528299)-   References: Saneyoshi, M., and Satoh, E., Synthetic Nucleosides and    Nucleotides. XIII. Stannic Chloride Catalyzed Ribosylation of    Several 6-Substituted Purines. Chem; Pharm. Bull., 27, 2518-2521    (1979).; Nakayama, C., and Saneyoshi, M., Synthetic Nucleosides and    Nucleotides. XX. Synthesis of Various    1-β-Xylofuranosyl-5-Alkyluracils and Related Nucleosides.    Nucleosides, Nucleotides, 1, 139-146 (1982).

Adenine (19.6 g, 144 mmol) was suspended in acetonitrile (400 ml) with1-O-acetyl-2,3,5-tri-O-benzoyl-β-L-ribofuranose 143 (60 g, 119 mmol). Tothis suspension was added stannic chloride fuming (22 ml, 187 mmol).After 12 hrs, the reaction was concentrated to a small volume (about 100ml), and sodium hydrogencarbonate (110 g) and water (120 ml) were added.The resulting white solid (tin salts) was extracted with hot chloroform(5×200 ml). The combined extracts were filtered on a cellite bed. Theorganic phase was washed with a NaHCO₃ 5% solution and water, dried oversodium sulfate, filtered and evaporated to give compound 144 (60 g,colorless foam). The foam was treated with methanol saturated withammonia (220 ml) in sealed vessel at room temperature under stirring for4 days. The solvent was evaporated off under reduced pressure and theresulting powder was suspended in ethyl acetate (400 ml) at reflux for 1hr. After filtration, the powder was recrystallized from water (220 ml)to give L-adenosine 145 (24 g, crystals, 75%)

Analyses for β-L-adenosine:

mp 233-234° C. (water) (lit. (4) mp 235°-238° C.) ¹H NMR (200 MHz,DMSO-D₆): δ 8.34 and 8.12 (2s, 2H, H₂ and H₈), 7.37 (1s, 2H, NH₂), 5.86(d, 1H, H_(1′), J_(1′,2′) 6.2 Hz), 5.43 (m, 2H, OH_(2′) and OH_(5′)),5.19 (d, 1H, OH_(3′), J 3.7 Hz), 4.60 (m, H_(2′)), 4.13 (m, 1H, H_(3′)),3.94 (m, 1H, H_(4′)), 3.69-3.49 (m, 2H, H_(5′a) and H_(5′b)), (identicalto commercial D-adenosine) Mass analysis (FAB+, GT) m/z 268 (M+H)⁺, 136(BH₂)⁺

Reaction 3:

-   Reactants: 1,3-Dichloro-1,1,3,3-tetraisopropyldisiloxane (Fluka; ref    36520); Sodium sulfate (Prolabo; ref 28111.365)-   Solvents: Pyridine 99% (Acros; ref 131780025); Ethyl acetate Pur    (Carlo erba; ref 528299); Acetonitrile (Riedel-de Haen; ref 33019)-   Reference: Robins, M. J., et al., Nucleic Acid Related    Compounds. 42. A General Procedure for the Efficient Deoxygenation    of Secondary Alcohols. Regiospecific and Stereoselective Conversion    of Ribonucleosides to 2′-Deoxynucleosides. J. Am. Chem. Soc. 105,    4059-4065 (1983).

To L-adenosine 145 (47.2 g, 177 mmol) suspended in pyridine (320 ml) wasadded 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane (63 ml, 201 mmol),and the mixture was stirred at room temperature for 12 hrs. Pyridine wasevaporated and the residue was partitioned with ethyl acetate (1 liter)and a NaHCO₃ 5% solution (600 ml). The organic phase was washed with aHCl 0.5N solution (2×500 ml) and water (500 ml), dried over sodiumsulfate, filtered and evaporated to dryness. The resulting solid wascrystallized from acetonitrile to give compound 146 (81 g, 90%).

Analyses 3′,5′-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanyl)-β-L-adenosine146:

mp 97-98° C. (acetonitrile) (lit. (5) D enantiomer mp 98° C.) ¹H NMR(200 MHz, CDCl₃): δ 8.28 and 7.95 (2s, 2H, H₂ and H₈), 5.96 (d, 1H,J_(1′,2′) 1.1 Hz), 5.63 (s, 2H, NH₂), 5.10 (dd, 1H, H_(3′), J_(3′,4′)7.6 Hz, J_(3′,2′) 5.5 Hz), 4.57 (dd, 1H, H_(2′), J_(2′,1′) 1.2 Hz;J_(2′,3′) 7.6 Hz), 4.15-3.99 (m, 3H, H_(4′), H_(5′a and H) _(5′b)), 3.31(sl, 1H, OH_(2′)), 1.06 (m, 28H, isopropyl protons) Mass analysis (FAB−,GT) m/z 508 (M−H)⁻, 134 (B)⁻; (FAB⁺, GT) m/z 510 (m+H)⁺, 136 (BH₂)⁺

Reaction 4:

-   Reactants: Dimethylaminopyridine 99% (Acros; ref 1482702050);    Phenylchlorothionocarbonate 99% (Acros; ref 215490050);    Tris(trimethylsilyl)silane “TTMSS” (Fluka; ref 93411);    α,α′-Azoisobutyronitrile “AIBN” (Fluka, ref 11630); Sodium sulfate    (Prolabo; ref 28111.365)-   Solvents: Acetonitrile (Riedel-de Haen; ref 33019); Ethyl acetate    Pur (Carlo Erba; ref 528299); Dioxan P.A. (Merck; ref 1.09671.1000);    Dichloromethane (Merck; ref 1.06050.6025); Methanol (Carlo Erba; ref    309002);-   Reference: Robins, M. J., Wilson, J. S., and Hansske, F., Nucleic    Acid Related Compounds. 42. A General Procedure for the Efficient    Deoxygenation of Secondary Alcohols. Regiospecific and    Stereoselective Conversion of Ribonucleosides to    2′-Deoxynucleosides. J. Am. Chem. Soc., 105, 4059-4065 (1983).

To compound 146 (34 g, 67 mmol) were added acetonitrile (280 ml), DMAP(16.5 g, 135 mmol) and phenyl chlorothionocarbonate (10.2 ml, 73 mmol).The solution was stirred at room temperature for 12 hrs. Solvent wasevaporated and the residue was partioned between ethyl acetate (400 ml)and a HCl 0.5N solution (400 ml). The organic layer was washed with aHCl 0.5N solution (400 ml) and water (2×400 ml), dried over sodiumsulfate, filtered and evaporated to dryness to give the intermediate asa pale yellow solid. The crude 147 was dissolved in dioxan (ml) and AIBN(3.3 g, 20 mmol) and TTMSS (33 ml, 107 mmol) were added. The solutionwas progressively heated until reflux and stirred for 2 hrs. Thereaction was concentrated to a yellow oil which was chromatographed(eluent dichloromethane/methanol 95/5) to give compound 148 (23 g,colorless foam, 70%). An aliquot was cristallized from ethanol/petroleumether.

Analyses for3′,5′-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanyl)-2′-deoxy-β-L-adenosine148:

mp 110-111° C. (EtOH/petroleum ether) (Lit. (5) mp 113-114° C. (EtOH))¹H NMR (200 MHz, CDCl₃): δ 8.33 and 8.03 (2s, 2H, H₂ and H₈), 6.30 (dd,1H, H_(1′), J 2.85 Hz, J 7.06 Hz), 5.63 (sl, 2H, NH₂), 4.96 (m, 1H,H_(3′)), 4.50 (m, 2H, H_(5′a) and H_(5′b)), 2.68 (m, 2H, H_(2′a) andH_(2′b)), 1.08 (m, 28H, isopropyl protons) Mass analysis (FAB+, GT) m/z494 (M+H)⁺, 136 (BH₂)⁺

Reaction 5:

-   Reactants: Ammonium fluoride (Fluka; ref 09742); Silica gel (Merck;    ref 1.07734.2500)-   Solvents: Methanol P.A. (Prolabo; ref 20847.295); Dichloromethane    P.A. (Merck; ref 1.06050.6025); Ethanol 95 (Prolabo; ref 20823.293)-   Reference: Zhang, W., and Robins, M. J., Removal of Silyl Protecting    Groups from Hydroxyl Functions with Ammonium Fluoride in Methanol.    Tetrahedron Lett., 33, 1177-1180 (192).

A solution of3′,5′-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanyl)-2′-deoxy-L-adenosine148 (32 g, 65 mmol) and ammonium fluoride (32 g, mmol) in methanol wasstirred at reflux for 2 hrs. Silica gel was added and the mixture wascarefully evaporated to give a white powder. This powder was added onthe top of a silica column, which was eluted withdichloromethane/methanol 9/1. The appropriate fractions were combinedand evaporated to give a white powder, which was crystallized fromethanol 95 (12.1 g, 75%).

Analyses for 2′-Deoxy-β-L-adenosine 149:

mp 189-190° C. (EtOH 95) (identical to commercial 2′-deoxy-D-adenosine)¹H NMR (200 MHz, DMSO-D₆): δ 8.35 and 8.14 (2s, 2H, H₂ and H₈), 7.34(sl, 2H, NH₂), 6.35 (dd, 1H, H_(1′), J 6.1 Hz, J 7.85 Hz), 5.33 (d, 1H,OH₂, J 4.0 Hz), 5.28 (dd, 1H, H_(3′), J 4.95 Hz; J 6.6 Hz), 4.42 (m, 1H,OH5′), 3.88 (m, 1H, H_(4′)), 3.63-3.52 (m, 2H, H_(5′a) and H_(5′b)),2.71 (m, 1H, H_(2′a)), 2.28 (m, 1H, H_(2′b)). (identical to commercial2′-deoxy-D-adenosine) α_(D)+26° (c 0.5 water) (commercial2′-deoxy-D-adenosine −25° (c 0.5 water)). UV λmax 260 nm (ε 14100)(H₂O). Mass analysis (FAB+, GT) m/z 252 (M+H)⁺, 136 (BH₂)⁺

EXAMPLE 3 Stereospecific Synthesis of 2′-Deoxy-β-L-Cytidine

1-(3,5-Di-O-benzoyl-β-L-xylofuranosyl)uracil (11)

Hydrazine hydrate (1.4 mL, 28.7 mmol) was added to a solution of1-(2-O-acetyl-3,5-di-O-benzoyl-β-L-xylofuranosyl) uracil 10 [Ref.:Gosselin, G.; Bergogne, M.-C.; Imbach, J.-L., “Synthesis and AntiviralEvaluation of β-L-Xylofuranosyl Nucleosides of the Five NaturallyOccurring Nucleic Acid Bases”, Journal of Heterocyclic Chemistry, 1993,30 (October-November), 1229-1233] (4.79 g, 9.68 mmol) in pyridine (60mL) and acetic acid (15 mL). The solution was stirred overnight at roomtemperature. Acetone was added (35 mL) and the mixture was stirred for30 min. The reaction mixture was evaporated under reduced pressure. Theresulting residue was purified by silica gel column chromatography[eluent: stepwise gradient of methanol (0-4%) in dichloromethane to give11 (3.0 g, 68%) which was crystallized from cyclohexane/dichloromethane:mp=111-114° C.; ¹H-NMR (DMSO-d₆): δ 11.35 (br s, 1H, NH), 7.9-7.4 (m,11H, 2 C₆H₅CO, H-6), 6.38 (d, 1H, OH-2′, J_(OH-2′)=4.2 Hz), 5.77 (d, 1H,H-1′, J_(1′-2′)=1.9 Hz), 5.55 (d, 1H, H-5, J₅₋₆=8 Hz), 5.54 (dd, 1H,H-3′, J_(3′-2′)=3.9 Hz and J_(3′-4′)=1.8 Hz), 4.8 (m, 1H, H-4′), 4.7 (m,2H, H-5′ and H-5″), 4.3 (m, 1H, H-2′); MS: FAB>0 (matrix GT) m/z 453(M+H)⁺, 105 (C₆H₅CO)⁺; FAB<0 (matrix GT) m/z 451 (M−H)⁻, 121 (C₆H₅CO₂)⁻,111 (B)⁻; Anal. Calcd for C₂₃H₂₀N₂O₈.H₂O: C, 58.09; H, 4.76; N, 5.96.Found: C, 57.71; H, 4.42; N, 5.70.

1-(3,5-Di-O-benzoyl-β-L-arabinofuranosyl)uracil (12)

To a solution of 1-(3,5-di-O-benzoyl-β-L-xylofuranosyl)uracil 11 (8 g,17.7 mL) in an anhydrous benzene-DMSO mixture (265 mL, 6:4, v/v) wereadded anhydrous pyridine (1.4 mL), dicyclohexylcarbodiimide (10.9 g, 53mmol) and dichloroacetic acid (0.75 mL). The resulting mixture wasstirred at room temperature for 4 h, then diluted with ethyl acetate(400 mL) and a solution of oxalic acid (4.8 g, 53 mmol) in methanol (14mL) was added. After being stirred for 1 h, the solution was filtered.The filtrate was washed with a saturated NaCl solution (2×500 mL), 3%NaHCO₃ solution (2×500 mL) and water (2×500 mL). The organic phase wasdried over Na₂SO₄, then evaporated under reduced pressure. The resultingresidue was then solubilized in an EtOH absolute-benzene mixture (140mL, 2:1, v/v). To this solution at 0° C. was added NaBH₄ (0.96 g, 26.5mmol). After being stirred for 1 h, the solution was diluted with ethylacetate (400 mL), then filtered. The filtrate was washed with asaturated NaCl solution (400 mL) and water (400 mL). The organic phasewas dried over Na₂SO₄, then evaporated under reduced pressure. Theresulting crude material was purified by silica gel columnchromatography [eluent: stepwise gradient of methanol (0-3%) indichloromethane to give 12 (5.3 g, 66%) which was crystallized fromacetonitrile: mp=182-183° C.; ¹H-NMR (DMSO-d₆): δ 11.35 (br s, 1H, NH),8.0-7.5 (m, 11H, 2 C₆H₅CO, H-6), 6.23 (br s, 1H, OH-2′), 6.15 (d, 1H,H-1′, J_(1′-2′)=4 Hz), 5.54 (d, 1H, H-5, J₅₋₆=8.1 Hz), 5.37 (t, 1H,H-3′, J_(3′-2′)=J_(3′-4′)=2.6 Hz), 4.7-4.6 (m, 2H, H-5′ and H-5″), 4.5(m, 1H, H-4′), 4.4 (m, 1H, H-2′); MS: FAB>0 (matrix GT) m/z 453 (M+H)⁺,341 (S)⁺, 113 (BH₂)⁺, 105 (C₆H₅CO)⁺; FAB<0 (matrix GT) m/z 451 (M−H)⁻,121 (C₆H₅CO₂)⁻, 111 (B)⁻; Anal. Calcd for C₂₃H₂₀N₂O₈: C, 61.06; H, 4.46;N, 6.19. Found: C, 60.83; H, 4.34; N, 6.25.

1-(3,5-Di-O-benzoyl-2-deoxy-β-L-erythro-pentofuranosyl)uracil (13)

To a solution of 1-(3,5-di-O-benzoyl-β-L-arabinofuranosyl)uracil 12 (5.2g, 11.4 mmoL) in anhydrous 1,2-dichloroethane (120 mL) were addedphenoxythiocarbonyl chloride (4.7 mL, 34.3 mL) and4-(dimethylamino)pyridine (DMAP, 12.5 g, 102.6 mmoL). The resultingsolution was stirred at room temperature under argon atmosphere for 1 hand then evaporated under reduced pressure. The residue was dissolved indichloromethane (300 mL) and the organic solution was successivelywashed with an ice-cold 0.2 N hydrochloric acid solution (3×200 mL) andwater (2×200 mL), dried over Na₂SO₄ then evaporated under reducedpressure. The crude material was co-evaporated several times withanhydrous dioxane and dissolved in this solvent (110 mL). To theresulting solution were added under argon tris-(trimethylsilyl)silanehydride (4.2 mL, 13.7 mmol) and α,α′-azoisobutyronitrile (AIBN, 0.6 g,3.76 mmol). The reaction mixture was heated and stirred at 100° C. for 1h under argon, then cooled to room temperature and evaporated underreduced pressure. The residue was purified by silica gel columnchromatography [eluent: stepwise gradient of methanol (0-5%)] to give 13(2.78 g, 56%) which was crystallized from EtOH: mp=223-225° C.; H-NMR(DMSO-d₆): δ 11.4 (br s, 1H, NH), 8.0-7.5 (m, 11H, 2 C₆H₅CO, H-6), 6.28(t, 1H, H-1′, J=7 Hz), 5.5 (m, 2H, H-1′ and H-5), 4.6-4.4 (m, 3H, H-4′,H-5′ and H-5″), 2.6 (m, 2H, H-2′ and H-2″); MS: FAB>0 (matrix GT) m/z437 (M+H)⁺, 3325 (S)⁺; FAB<0 (matrix GT) m/z 435 (M−H)⁻, 111 (B)⁻; Anal.Calcd for C₂₃H₂₀N₂O₇: C, 63.30; H, 4.62; N, 6.42. Found: C, 62.98; H,4.79; N, 6.40.

2′-Deoxy-β-L-cytidine (β-L-dC)

Lawesson's reagent (1.72 g, 4.26 mmol) was added under argon to asolution of1-(3,5-di-O-benzoyl-2-deoxy-β-L-erythro-pentofuranosyl)uracil 13 (2.66g, 6.1 mmol) in anhydrous 1,2-dichloroethane (120 mL) and the reactionmixture was stirred under reflux for 2 h. The solvent was thenevaporated under reduced pressure and the residue was purified by silicagel column chromatography [eluent: stepwise gradient of ethyl acetate(0-8%) in dichloromethane] to give the 4-thio intermediate as a yellowfoam. A solution of this thio-intermediate (1.5 g, 3.31 mmol) inmethanolic ammonia (previously saturated at −10° C. and tightly stopped)(50 mL) was heated at 100° C. in a stainless-steel bomb for 3 h and thencooled to 0° C. The solution was evaporated under reduced pressure. Theresulting crude material was purified by silica gel columnchromatography [eluent: stepwise gradient of methanol (0-20%) indichloromethane]. Finally, the appropriate fractions were pooled,filtered through a unit Millex HV-4 (0.45 μm, Millipore) and evaporatedunder reduced pressure to provide the desired 2′-deoxy-β-L-cytidine(β-L-dC) as a foam (0.6 g, 80%) which was crystallized from absoluteEtOH: mp=198-199° C.; ¹H-NMR (DMSO-d₆): δ 7.77 (d, 1H, H-6, J₆₋₅=7.4Hz), 7.10 (br d, 2H, NH-₂), 6.13 (t, 1H, H-1′, J=6.7 Hz), 5.69 (d, 1H,H-5, J₅₋₆=7.4 Hz), 5.19 (d, 1H, OH-3′, J_(OH-3′)=4.1 Hz), 4.96 (t, 1H,OH-5′, J_(OH-5′)=J_(OH-5″)=5.2 Hz), 4.1 (m, 1H, H-3′), 3.75 (m, 1H,H-4′), 3.5 (m, 2H, H-5′ and H-5″), 2.0 (m, 1H, H-2′), 1.9 (m, 1H, H-2″);MS: FAB>0 (matrix GT) m/z 228 (M+H)⁺, 112 (BH₂)⁺; FAB<0 (matrix GT) m/z226 (M−H)⁻; [α]²⁰ _(D)=−69 (c 0.52, DMSO) [[α]²⁰ _(D)=+76 (c 0.55, DMSO)for a commercially available hydrochloride salt of the D-enantiomer].Anal. Calcd for C₉H₁₃N₃O₄: C, 47.57; H, 5.77; N, 18.49. Found: C, 47.35;H, 5.68; N, 18.29.

EXAMPLE 4 Stereoselective Synthesis of 2′-Deoxy-β-L-Cytidine (β-L-dC)

2-Amino-β-L-arabinofurano[1′,2′:4,5]oxazoline (1)

A mixture of L-arabinose (170 g, 1.13 mol), cyanamide (100 g, 2.38 mol),methanol (300 ml), and 6M-NH₄OH (50 ml) was stirred at room temperaturefor 3 days and then kept at −10° C. overnight. The product was collectedwith suction, washed successively with methanol and ether, and dried invacuo. Yield, 130 g (66.0%) of the analytically pure compound 1, m.p.170-172° C.; ¹H NMR (DMSO-d₆) δ ppm 6.35 (br s, 2H, NH₂), 5.15 (d, 1H,H-1, J=5.6 Hz), 5.45 (br s, 1H, OH-3), 4.70 (br s, 1H, OH-5), 4.55 (d,1H, H-2, J=5.6 Hz), 4.00 (br s, 1H, H-3), 3.65 (m, 1H, H-4), 3.25 (m,2H, H-5, H-5′).

Reagents:

-   L-arabinose: Fluka, >99.5%, ref 10839-   Cyanamide: Fluka, >98%, ref 28330    O^(2,2′)-anhydro-β-L-uridine (2)

A solution of compound 1 (98.8 g, 0.57 mol) and methyl propiolate (98ml) in 50% aqueous ethanol (740 ml) was refluxed for 5 h, then cooledand concentrated under diminished pressure to the half of the originalvolume. After precipitation with acetone (600 ml), the product wascollected with suction, washed with ethanol and ether, and dried. Themother liquor was partially concentrated, the concentrate precipitatedwith acetone (1000 ml), the solid collected with suction, and washedwith acetone and ether to afford another crop of the product. Over-allyield, 80 g (62%) of compound 2, m.p. 236-240° C.; ¹H NMR (DMSO-d₆) δppm 7.87 (d, 1H, H-6, J=7.4 Hz), 6.35 (d, 1H, H-1′, J=5.7 Hz), 5.95 (d,1H, H-5, J=7.4 Hz), 5.90 (d, 1H, OH-3′), 5.20 (d, 1H, H-2′, J=5.7 Hz),5.00 (m, 1H, OH-3′), 4.44 (br s, 1H, H-3′), 4.05 (m, 1H, H-4′), 3.25 (m,2H, H-5, H-5′).

Reagent:

-   Methyl propiolate: Fluka, >97%, ref 81863    3′,5′-Di-O-benzoyl-O^(2,2′)-anhydro-β-L-uridine (3)

To a solution of compound 2 (71.1 g, 0.31 mol) in anhydrous pyridine(1200 ml) was added benzoyl chloride (80.4 ml) at 0° C. and under argon.The reaction mixture was stirred at room temperature for 5 h underexclusion of atmospheric moisture and stopped by addition of ethanol.The solvents were evaporated under reduced pressure and the resultingresidue was coevaporated with toluene and absolute ethanol. The crudemixture was then diluted with ethanol and the precipitate collected withsuction, washed successively with ethanol and ether, and dried. Yield,129 g (95.8%) of compound 3, m.p. 254° C.; ¹H NMR (DMSO-d₆) δ ppm8.1-7.4 (m, 11H, C₆H₅CO, H-6), 6.50 (d, 1H, H-1′, J=5.7 Hz), 5.90 (d,1H, H-5, J=7.5 Hz), 5.80 (d, 1H, H-2′, J=5.8 Hz), 5.70 (d, 1H, H-3′)4.90 (m, 1H, H-4′), 4.35 (m, 2H, H-5, H-5′).

Reagent:

-   Benzoyl chloride: Fluka, p.a., ref 12930    3′,5′-Di-O-benzoyl-2′-chloro-2′-deoxy-β,L-uridine (4)

To a solution of compound 3 (60.3 g, 0.139 mol) in dimethylformamide(460 ml) was added at 0° C. a 3.2 N—HCl/DMF solution (208 ml, preparedin situ by adding 47.2 ml of acetyl chloride at 0° C. to a solution of27.3 ml of methanol and 133.5 ml of dimethylformamide). The reactionmixture was stirred at 100° C. for 1 h under exclusion of atmosphericmoisture, cooled down, and poured into water (4000 ml). The precipitateof compound 4 was collected with suction, washed with water, andrecrystallised from ethanol. The crystals were collected, washed withcold ethanol and ether, and dried under diminished pressure. Yield, 60.6g (92.6%) of compound 4, m.p. 164-165° C.; ¹H NMR (DMSO-d₆) δ ppm 8.7(br s, 1H, NH), 8.1-7.3 (m, 11H, C₆H₅CO, H-6), 6.15 (d, 1H, H-1′, J=4.8Hz), 5.5 (m, 2H, H-5, H-2′), 4.65 (m, 4H, H-3′, H-4′, H-5′, H-5″).

Reagent:

-   Acetyl chloride: Fluka, p.a., ref 00990    3′,5′-Di-O-benzoyl-2′-deoxy-β,L-uridine (5)

A mixture of compound 4 (60.28 g, 0.128 mol), tri-n-butyltin hydride (95ml) and azabisisobutyronitrile (0.568 g) in dry toluene (720 ml) wasrefluxed under stirring for 5 h and cooled down. The solid was collectedwith suction and washed with cold toluene and petroleum ether. Thefiltrate was concentrated under reduced pressure and diluted withpetroleum ether to deposit an additional crop of compound 5. Yield,54.28 g (97.2%) of compound 5; m.p. 220-221° C.; ¹H NMR (CDCl₃) δ ppm8.91 (br s, 1H, NH), 8.1-7.5 (m, 11H, C₆H₅CO and H-6), 6.43 (q, 1H,H-1′, J_(1′,2′)=5.7 Hz and J_(1′,2″)=8.3 Hz), 5.7-5.6 (m, 2H, H-3′ andH-5), 4.8-4.6 (m, 3H, H-5′, H-5″ and H-4′), 2.8-2.7 (m, 1H, H-2′),2.4-2.3 (m, 1H, H-2″).

Reagents:

-   Tri-n-butyltin hydride: Fluka, >98%, ref 90915-   Azabisisobutyronitrile: Fluka, >98%, ref 11630    3′,5′-Di-O-benzoyl-2′-deoxy-β-L-4-thio-uridine (6)

A solution of compound 5 (69 g, 0.158 mol) and Lawesson's reagent (74 g)in anhydrous methylene chloride (3900 ml) was refluxed under argonovernight. After evaporation of the solvant, the crude residue waspurified by a silica gel column chromatography [eluant: gradient ofmethanol (0-2%) in methylene chloride] to afford pure compound 6 (73 g)in quantitative yield; ¹H NMR (CDCl₃) δ ppm 9.5 (br s, 1H, NH), 8.1-7.4(m, 10H, C₆H₅CO), 7.32 (d, 1H, H-6, J=7.7 Hz), 6.30 (dd, 1H, H-1′, J=5.6Hz and J=8.2 Hz), 6.22 (d, 1H, H-5, J=7.7 Hz), 5.6 (m, 1H, H-3′), 4.7(m, 2H, H-5′, H-5″), 4.5 (m, 1H, H-4′), 2.8 (m, 1H, H-2′), 2.3 (m, 1H,H-2″).

Reagent:

-   Lawesson's reagent: Fluka, >98%, ref 61750    2′-Deoxy-β-L-cytosine

A solution of compound 6 (7.3 g, 0.016 mol) in methanol saturated withammonia (73 ml) was heated at 100° C. in a stainless steel cylinder for3 h. After cooling carefully, the solvent was evaporated under reducedpressure. An aqueous solution of the residue was washed with ethylacetate and evaporated to dryness. Such a procedure was carried out on 9other samples (each 7.3 g) of compound 6 (total amount of 6=73 g). The10 residues were combined, diluted with absolute ethanol and cooled togive 7 as crystals. Trace of benzamide were eliminated from the crystalsof 6 by a solid-liquid extraction procedure (at reflux in ethyl acetatefor 1 h). Yield, 28.75 g (78.6%) of compound 6; m. p. 141-145° C.; ¹HNMR (DMSO) δ ppm 8.22 and 8.00 (2 br s, 2H, NH₂), 7.98 (d, 1H, H-6,J=7.59 Hz), 6.12 (t, 1H, H-1′, J=6.5 Hz and J=7.6 Hz), 5.89 (d, 1H, H-5,J=7.59 Hz), 5.3 (br s, 1H, OH-3′), 5.1 (br s, 1H, OH-5′), 4.2 (m, 1H,H-3′), 3.80 (q, 1H, H-4′, J=3.6 Hz and J=6.9 Hz), 3.6-3.5 (m, 2H, H-5′,H-5″), 2.2-2.0 (m, 2H, H-2′, H-2″); FAB<0, (GT) m/e 226 (M−H)⁻, 110(B)⁻; FAB>0 (GT) 228 (M+H)⁺, 112 (B+2H)⁺; [α]_(D) ²⁰−56.48 (c=1.08 inDMSO); UV (pH 7) λ_(max)=270 nm (ε=10000).

Reagent:

-   Methanolic ammonia: previously saturated at −5° C., tightly    stoppered, and kept in a freezer.

EXAMPLE 5 Stereoselective Synthesis of 2′-Deoxy-β-L-Thymidine (β-L-dT)

3′,5′-Di-O-benzoyl-2′-deoxy-5-iodo-β-L-uridine (7)

A mixture of compound 5 (105.8 g, 0.242 mol), iodine (76.8 g), CAN (66.4g) and acetonitrile (2550 ml) was stirred at 80° C. for 3 h then thereaction mixture was cooled at room temperature leading tocrystallization of compound 7 (86.6 g, 63.5%); m. p. 192-194° C.; ¹H NMR(DMSO) δ ppm. 8.34 (s, 1H, NH), 8.2-7.2 (m, 11H, 2 C₆H₅CO, H-6), 6.31(q, 1H, H-1′, J=5.5 Hz and J=8.7 Hz), 5.5 (m, 1H, H-3′), 4.7 (m, 2H,H-5′, H-5″), 4.5 (m, 1H, H-4′), 2.7 (m, 1H, H-2′), 2.3 (m, 1H, H-2″);FAB<0, (GT) m/e 561 (M−H)⁻, 237 (B)⁻; FAB>0 (GT) 563 (M+H)⁺; [α]_(D)²⁰+39.05 (c=1.05 in DMSO); UV (EtOH 95) υ_(max)=281 nm (ε=9000),υ_(min)=254 nm (ε=4000), υ_(max)=229 nm (ε=31000); Anal. Calcd forC₂₃H₁₉IN₂O₇: C, 49.13; H, 3.41; N, 4.98; I, 22.57. Found: C, 49.31; H,3.53; N, 5.05; I, 22.36.

Reagents:

-   Iodine: Fluka, 99.8%, ref 57650-   Cerium ammonium nitrate (CAN): Aldrich, >98.5%, ref 21,547-3    3′,5′-Di-O-benzoyl-2′-deoxy-3-N-toluoyl-β-L-thymidine (9)

To a solution of compound 7 (86.6 g, 0.154 mol) in anhydrous pyridine(1530 ml) containing N-ethyldiisopropylamine (53.6 ml) was added,portionwise at 0° C., p-toluoyl chloride (40.6 ml). The reaction mixturewas stirred for 2 h at room temperature, then water was added to stopthe reaction and the reaction mixture was extracted with methylenechloride. The organic phase was washed with water, dried over sodiumsulfate and evaporated to dryness to give crude3′,5′-di-O-benzoyl-2′-deoxy-3-N-toluoyl-5-iodo-β-L-uridine (8) which canbe used for the next step without further purification.

A solution of the crude mixture 8, palladium acetate (3.44 g),triphenylphosphine (8.0 g) in N-methylpyrrolidinone (1375 ml) withtriethylamine (4.3 ml) was stirred at room temperature for 45 min. Then,tetramethyltin (42.4 ml) was added dropwise at 0° C. under argon. Afterstirring at 100-110° C. overnight, the reaction mixture was poured intowater and extracted with diethyl ether. The organic solution was driedover sodium sulfate and concentrated under reduced pressure. The residuewas purified by a silica gel column chromatography [eluant: stepwisegradient of ethyl acetate (0-10%) in toluene] to give compound 9 as afoam (42.3 g, 48.3% for the 2 steps). ¹H NMR (DMSO) δ ppm. 8.3-7.2 (m,15H, 2 C₆H₅CO, 1 CH₃C₆H₄CO, H-6), 6.29 (t, 1H, H-1′, J=7.0 Hz), 5.7 (m,1H, H-3′), 4.7-4.5 (m, 3H, H-5′, H-5″, H-4′), 2.7-2.6 (m, 2H, H-2′,H-2″); FAB<0, (GT) m/e 567 (M−H)⁻, 449 (M-CH₃C₆H₄CO)⁻, 243 (B)⁻, 121(C₆H₅COO)—; FAB>0 (GT) 1137 (2M+H)⁺, 569 (M+H)⁺, 325 (M−B)⁻, 245(B+2H)⁺, 19 (CH₃C₆H₅CO)⁺.

Reagents:

-   p-Toluoyl chloride, Aldrich, 98%, ref 10, 663-1-   Diisopropylethylamine: Aldrich, >99.5%, ref 38,764-9-   N-methylpyrrolidinone: Aldrich, >99%, ref 44, 377-8-   Paladium acetate: Aldrich, >99.98%, ref 37, 987-5-   Triphenylphosphine: Fluka, >97%, ref 93092-   Tetramethyltin: Aldrich, >99%, ref 14,647-1    2′-Deoxy-β-L-thymidine

A solution of compound 9 (42.3 g, 0.074 mol) in methanol saturated withammonia (1850 ml) was stirred at room temperature for two days. Afterevaporation of the solvent, the residue was diluted with water andwashed several times with ethyl acetate. The aqueous layer wasseparated, evaporated under reduced pressure and the residue waspurified by a silica gel column chromatography [eluant: stepwisegradient of methanol (0-10%) in methylene chloride] to give pure2′-deoxy-β-L-thymidine (11.62 g, 64.8%) which was crystallized fromethanol; m.p. 185-188° C.; ¹H NMR (DMSO) δ ppm 11.3 (s, 1H, NH), 7.70(s, 1H, H-6), 6.2 (pt, 1H, H-1′), 5.24 (d, 1H, OH-3′, J=4.2 Hz), 5.08(t, 1H, OH-5′, J=5.1 Hz), 4.2 (m, 1H, H-3′), 3.7 (m, 1H, H-4′), 3.5-3.6(m, 2H, H-5′, H-5″), 2.1-2.0 (m, 2H, H-2′, H-2″); FAB<0, (GT) m/e 483(2M−H)⁻, 349 (M+T−H)⁻, 241 (M−H)⁻, 125 (B)⁻; FAB>0 (GT) 243 (M+H)⁺, 127(B+2H)⁺;)⁺; [α]_(D) ²⁰−13.0 (c=1.0 in DMSO); UV (pH 1) υ_(max)=267 nm(ε=9700), υ_(min)=234 nm (ε=2000).

Reagent:

-   Methanolic ammonia: previously saturated at −5° C., tightly    stoppered, and kept in a freezer.

EXAMPLE 6 Stereoselective Synthesis of 2′-deoxy-β-L-inosine (β-L-dI)

β-L-dI was synthesized by deamination of 2′-deoxy-β-L-adenosine (β-L-dA)following a procedure previously described in the 9-D-glucopyranosylseries (Ref: I. Iwai, T. Nishimura and B. Shimizu, Synthetic Proceduresin Nucleic Acid Chemistry, W. W. Aorbach and R. S. Tipson, eds., JohnWiley & Sons, Inc. New York, vol. 1, pp. 135-138 (1968)).

Thus, a solution of β-L-DA (200 mg) in a mixture of acetic acid (0.61ml) and water (19 ml) was heated with sodium nitrite (495 mg), and themixture was stirred at room temperature overnight. The solution was thenevaporated to dryness under diminished pressure. An aqueous solution ofthe residue was applied to a column of IR-120 (H⁺) ion-exchange resin,and the column was eluted with water. Appropriate fractions werecollected and evaporated to dryness to afford pure β-L-dI which wascrystallized from methanol (106 mg, 53% yield not optimized):m.p.=209°-211° C.; UV (H₂O), λ_(max)=247 nm; ¹H-NMR (DMSO-d₆)=8.32 and8.07 (2s, 1H each, H-2 and H-8), 6.32 (pt, 1H, H-1; J=6.7 Hz), 4.4 (m,1H, H-3′), 3.9 (m, 1H, H-4′), 3.7-3.4 (m, 2H partially obscured by HOD,H-5′,5″), 2.6 and 2.3 (2m, 1H each, H-2′ and H-2″); mass spectra(mature, glycerol-thioglycerol, 1:1, v/v), FAB>0: 253 (m+H)⁺, 137(base+2H)⁺; FAB<0: 251 (m−H)⁻, 135 (base)⁻; [α]_(D) ²⁰=+19.3 (−c 0.88,H₂O).

Anti-HBV Activity of the Active Compounds

The ability of the active compounds to inhibit the growth of virus in2.2.15 cell cultures (HepG2 cells transformed with hepatitis virion) canbe evaluated as described in detail below.

A summary and description of the assay for antiviral effects in thisculture system and the analysis of HBV DNA has been described (Korba andMilman, 1991, Antiviral Res., 15:217). The antiviral evaluations areperformed on two separate passages of cells. All wells, in all plates,are seeded at the same density and at the same time.

Due to the inherent variations in the levels of both intracellular andextracellular HBV DNA, only depressions greater than 3.5-fold (for HBVvirion DNA) or 3.0-fold (for HBV DNA replication intermediates) from theaverage levels for these HBV DNA forms in untreated cells are consideredto be statistically significant (P<0.05). The levels of integrated HBVDNA in each cellular DNA preparation (which remain constant on a percell basis in these experiments) are used to calculate the levels ofintracellular HBV DNA forms, thereby ensuring that equal amounts ofcellular DNA are compared between separate samples.

Typical values for extracellular HBV virion DNA in untreated cells rangefrom 50 to 150 pg/ml culture medium (average of approximately 76 pg/ml).Intracellular HBV DNA replication intermediates in untreated cells rangefrom 50 to 100 μg/pg cell DNA (average approximately 74 pg/μg cell DNA).In general, depressions in the levels of intracellular HBV DNA due totreatment with antiviral compounds are less pronounced, and occur moreslowly, than depressions in the levels of HBV virion DNA (Korba andMilman, 1991, Antiviral Res., 15:217).

The manner in which the hybridization analyses are performed for theseexperiments result in an equivalence of approximately 1.0 pg ofintracellular HBV DNA to 2-3 genomic copies per cell and 1.0 pg/ml ofextracellular HBV DNA to 3×10⁵ viral particles/ml.

EXAMPLE 7

The ability of the triphosphate derivatives of β-L-dA, β-L-dC, β-L-dU,β-L-2′-dG, β-L-dI, and β-L-dT to inhibit hepatitis B was tested. Table 1describes the comparative inhibitory activities of triphosphates ofβ-L-dT (β-L-dT-TP), 13-L-dC (β-L-dC-TP), β-L-dU (β-L-dU-TP) and β-L-dA(β-L-dA-TP) on woodchuck hepatitis virus (WHV) DNA polymerase, human DNApolymerases α, β, and γ.

TABLE 1 WHV DNA pol DNA pol α DNA pol β DNA pol γ Inhibitor IC₅₀ K_(i)^(b) (μM) K_(i) ^(b) (μM) K_(i) ^(b) (μM) β-L-dT-TP 0.34 >100 >100 >100β-L-dA-TP 2.3 >100 >100 >100 β-L-dC-TP 2.0 >100 >100 >100 β-L-dU-TP8 >100 >100 >100 ^(a)IC₅₀: 50% Inhibitory concentration ^(b)K_(i) valuewas determined using calf thymus activated DNA as template-primer anddATP as substrate. Inhibitors were analyzed by Dixon plot analysis.Under these conditions, the calculated mean K_(m) of human DNApolymerase α for dATP as approximately 2.6 μM. Human DNA polymerase βexhibited a steady state K_(m) of 3.33 μM for dATP. Human DNA polymeraseγ exhibited a steady K_(m) of 5.2 μM.

EXAMPLE 8

The anti-hepatitis B virus activity of β-L-dA, β-L-dC, β-L-dU, β-L-2′-dGand β-L-dT was tested in transfected Hep G-2 (2.2.15) cells. Table 2illustrates the effect of β-L-dA, β-L-dC, β-L-dU, and β-L-dT againsthepatitis B virus replication in transfected Hep G-2 (2.2.15) cells.

TABLE 2 Selectivity HBV virions^(a) HBV Ri^(b) Cytotoxicity IndexCompound EC₅₀ (μM) EC₅₀ (μM) IC₅₀ (μM) IC₅₀/EC₅₀ β-L-dT 0.050.05 >200 >4000 β-L-dC 0.05 0.05 >200 >4000 β-L-dA 0.10 0.10 >200 >2000β-L-dI 1.0 1.0 >200 >200 β-L-dU 5.0 5.0 >200 >40 ^(a)Extracellular DNA^(b)Replicative intermediates (Intracellular DNA)

EXAMPLE 9

The effect of β-L-dA, β-L-dC and β-L-dT in combination on the growth ofhepatitis B was measured in 2.2.15 cells. The results are provided inTable 3.

TABLE 3 Combination Ratio EC₅₀ L-dC + L-dT 1:3 .023 L-dC + L-dT 1:1 .053L-dC + L-dT 3:1 .039 L-dC + L-dA  1:30 .022 L-dC + L-dA  1:10 .041L-dC + L-dA 1:3 .075 L-dT + L-dA  1:30 .054 L-dT + L-dA  1:10 .077L-dT + L-dA 1:3 .035

Each combination produced anti-HBV activity that was synergistic. Inaddition, the combination of L-dA+L-dC+L-dT was also synergistic in thismodel.

EXAMPLE 10

The inhibition of hepatitis B replication in 2.2.15 cells by β-L-DA andβ-L-dC, alone and in combination was measured. The results are shown inTable 4.

TABLE 4 ^(a)β-L-2′-deoxy- ^(b)β-L-2′-deoxy- adenosine (μM) cytidine (μM)% Inhibition ^(c)C.I. 0.5 90 0.05 24 0.005 1 0.5 95 0.05 40 0.005 100.05 0.05 80 0.34 0.05 0.005 56 0.20 0.05 0.0005 50 0.56 0.005 0.05 720.35 0.005 0.005 54 0.35 0.005 0.0005 30 0.16 0.0005 0.05 50 0.83 0.00050.005 15 0.28 0.0005 0.0005 0 N.A. ^(a)β-L-2′-deoxy-adenosine: IC₅₀ =0.09 μM ^(b)β-L-2′-deoxy-cytidine: IC₅₀ = 0.06 μM ^(c)Combinationindices values indicate synergism effect (<1), additive effect (=1), andantagonism effect (>1)

EXAMPLE 11

The efficacy of L-dA, L-dT and L-dC against hepadnavirus infection inwoodchucks (Marmota monax) chronically infected with woodchuck hepatitisvirus (WHV) was determined. This animal model of HBV infection is widelyaccepted and has proven to be useful for the evaluation of antiviralagents directed against HBV.

Protocol:

Experimental groups (n = 3 animals/drug group, n = 4 animals/control)Group 1 vehicle control Group 2 lamivudine (3TC) (10 mg/kg/day) Groups3-6 L-dA (0.01, 0.1, 1.0, 10 mg/kg/day) Groups 7-10 L-dT (0.01, 0.1,1.0, 10 mg/kg/day) Groups 11-14 L-dC (0.01, 0.1, 1.0, 10 mg/kg/day)

Drugs were administered by oral gavage once daily, and blood samplestaken on days 0, 1, 3, 7, 14, 21, 28, and on post-treatment days +1, +3,+7, +14, +28 and +56. Assessment of the activity and toxicity was basedon the reduction of WHV DNA in serum: dot-blot, quantitative PCR.

The results are illustrated in FIG. 3 and Table 5.

TABLE 5 Antiviral Activity of LdA, LdT, LdC in Woodchuck Model ofChronic HBV Infection Control LdA LdT LdC day ng WHV-DNA per mlserum^(1,2) 0 381 436 423 426 1 398 369 45 123 3 412 140 14 62 7 446 1026 46 14 392 74 1 20 ¹LdA, LdT, LdC administered orally once a day at 10mg/kg ²limit of detection is 1 ng/ml WHV-DNA per ml serum

The data show that L-dA, L-dT and L-dC are highly active in this in vivomodel. First, viral load is reduced to undetectable (L-dT) or nearlyundetectable (L-dA, L-dC) levels. Second, L-dA, L-dT and L-dC are shownto be more active than 3TC (lamivudine) in this model. Third, viralrebound is not detected for at least two weeks after withdrawal of L-dT.Fourth, dose response curves suggest that a modes increase in the doseof L-dA and L-dC would show antiviral activity similar to L-dT. Fifth,all animals receiving the drugs gained weight and no drug-relatedtoxicity was detected.

EXAMPLE 12 Chemical Synthesis of β-L-dC 5′-L-Valyl Ester

As an illustrative example of the synthesis of β-L-dC amino esters,β-L-dC 5′-L-valyl ester is synthesized by first protecting the aminegroup of 13-L-dC using (CH₃)₃SiCl. The protected β-L-dC undergoesesterification by the addition of N-Boc L-valine. The ester is thendeprotected to yield β-L-dC 5′-L-valyl ester. Other methods forsynthesizing amino acid esters are disclosed in U.S. Pat. Nos. 5,700,936and 4,957,924, incorporated herein by reference. The L-valinyl5′-O-ester of L-dA, L-dC, L-dT, and L-dU are preferred embodiments ofthis invention.

Toxicity of Compounds

Toxicity analyses were performed to assess whether any observedantiviral effects are due to a general effect on cell viability. Themethod used is the measurement of the effect of 3-L-dA, β-L-dC andβ-L-dT on cell growth in human bone marrow clorogenic assays, ascompared to Lamuvidine. The results are provided in Table 6.

TABLE 6 Compound CFU-GM (μM) BFU-E (μM) β-L-dA >10 >10 β-L-dC >10 >10β-L-dT >10 >10 β-L-dU >10 >10 Lamuvidine >10 >10Preparation of Pharmaceutical Compositions

Humans suffering from any of the disorders described herein, includinghepatitis B, can be treated by administering to the patient an effectiveamount of a β-2′-deoxy-β-L-erythro-pentofuranonucleoside, for example,β-L-2′-deoxyadenosine, β-L-2′-deoxycytidine, β-L-2′-deoxyuridine,β-L-2′-deoxyguanosine or β-L-2′-deoxythymidine or a pharmaceuticallyacceptable prodrug or salt thereof in the presence of a pharmaceuticallyacceptable carrier or diluent. The active materials can be administeredby any appropriate route, for example, orally, parenterally,intravenously, intradermally, subcutaneously, or topically, in liquid orsolid form.

The active compound is included in the pharmaceutically acceptablecarrier or diluent in an amount sufficient to deliver to a patient atherapeutically effective amount of compound to inhibit viralreplication in vivo, without causing serious toxic effects in thepatient treated. By “inhibitory amount” is meant an amount of activeingredient sufficient to exert an inhibitory effect as measured by, forexample, an assay such as the ones described herein.

A preferred dose of the compound for all of the abovementionedconditions will be in the range from about 1 to 50 mg/kg, preferably 1to 20 mg/kg, of body weight per day, more generally 0.1 to about 100 mgper kilogram body weight of the recipient per day. The effective dosagerange of the pharmaceutically acceptable prodrug can be calculated basedon the weight of the parent nucleoside to be delivered. If the prodrugexhibits activity in itself, the effective dosage can be estimated asabove using the weight of the prodrug, or by other means known to thoseskilled in the art.

The compound is conveniently administered in unit any suitable dosageform, including but not limited to one containing 7 to 3000 mg,preferably 70 to 1400 mg of active ingredient per unit dosage form. Aoral dosage of 50-1000 mg is usually convenient.

Ideally the active ingredient should be administered to achieve peakplasma concentrations of the active compound of from about 0.2 to 70 μM,preferably about 1.0 to 10 μM. This may be achieved, for example, by theintravenous injection of a 0.1 to 5% solution of the active ingredient,optionally in saline, or administered as a bolus of the activeingredient.

The concentration of active compound in the drug composition will dependon absorption, inactivation, and excretion rates of the drug as well asother factors known to those of skill in the art. It is to be noted thatdosage values will also vary with the severity of the condition to bealleviated. It is to be further understood that for any particularsubject, specific dosage regimens should be adjusted over time accordingto the individual need and the professional judgment of the personadministering or supervising the administration of the compositions, andthat the concentration ranges set forth herein are exemplary only andare not intended to limit the scope or practice of the claimedcomposition. The active ingredient may be administered at once, or maybe divided into a number of smaller doses to be administered at varyingintervals of time.

A preferred mode of administration of the active compound is oral. Oralcompositions will generally include an inert diluent or an ediblecarrier. They may be enclosed in gelatin capsules or compressed intotablets. For the purpose of oral therapeutic administration, the activecompound can be incorporated with excipients and used in the form oftablets, troches, or capsules. Pharmaceutically compatible bindingagents, and/or adjuvant materials can be included as part of thecomposition.

The tablets, pills, capsules, troches and the like can contain any ofthe following ingredients, or compounds of a similar nature: a bindersuch as microcrystalline cellulose, gum tragacanth or gelatin; anexcipient such as starch or lactose, a disintegrating agent such asalginic acid, Primogel, or corn starch; a lubricant such as magnesiumstearate or Sterotes; a glidant such as colloidal silicon dioxide; asweetening agent such as sucrose or saccharin; or a flavoring agent suchas peppermint, methyl salicylate, or orange flavoring. When the dosageunit form is a capsule, it can contain, in addition to material of theabove type, a liquid carrier such as a fatty oil. In addition, dosageunit forms can contain various other materials which modify the physicalform of the dosage unit, for example, coatings of sugar, shellac, orother enteric agents.

The compound can be administered as a component of an elixir,suspension, syrup, wafer, chewing gum or the like. A syrup may contain,in addition to the active compounds, sucrose as a sweetening agent andcertain preservatives, dyes and colorings and flavors.

The compound or a pharmaceutically acceptable derivative or saltsthereof can also be mixed with other active materials that do not impairthe desired action, or with materials that supplement the desiredaction, such as antibiotics, antifungals, antiinflammatories, proteaseinhibitors, or other nucleoside or nonnucleoside antiviral agents.Solutions or suspensions used for parenteral, intradermal, subcutaneous,or topical application can include the following components: a sterilediluent such as water for injection, saline solution, fixed oils,polyethylene glycols, glycerine, propylene glycol or other syntheticsolvents; antibacterial agents such as benzyl alcohol or methylparabens; antioxidants such as ascorbic acid or sodium bisulfite;chelating agents such as ethylenediaminetetraacetic acid; buffers suchas acetates, citrates or phosphates and agents for the adjustment oftonicity such as sodium chloride or dextrose. The parental preparationcan be enclosed in ampoules, disposable syringes or multiple dose vialsmade of glass or plastic.

If administered intravenously, preferred carriers are physiologicalsaline or phosphate buffered saline (PBS).

In a preferred embodiment, the active compounds are prepared withcarriers that will protect the compound against rapid elimination fromthe body, such as a controlled release formulation, including implantsand microencapsulated delivery systems. Biodegradable, biocompatiblepolymers can be used, such as ethylene vinyl acetate, polyanhydrides,polyglycolic acid, collagen, polyorthoesters, and polylacetic acid.Methods for preparation of such formulations will be apparent to thoseskilled in the art. The materials can also be obtained commercially fromAlza Corporation.

Liposomal suspensions (including liposomes targeted to infected cellswith monoclonal antibodies to viral antigens) are also preferred aspharmaceutically acceptable carriers. These may be prepared according tomethods known to those skilled in the art, for example, as described inU.S. Pat. No. 4,522,811 (which is incorporated herein by reference inits entirety). For example, liposome formulations may be prepared bydissolving appropriate lipid(s) (such as stearoyl phosphatidylethanolamine, stearoyl phosphatidyl choline, arachadoyl phosphatidylcholine, and cholesterol) in an inorganic solvent that is thenevaporated, leaving behind a thin film of dried lipid on the surface ofthe container. An aqueous solution of the active compound or itsmonophosphate, diphosphate, and/or triphosphate derivatives is thenintroduced into the container. The container is then swirled by hand tofree lipid material from the sides of the container and to disperselipid aggregates, thereby forming the liposomal suspension.

This invention has been described with reference to its preferredembodiments. Variations and modifications of the invention, will beobvious to those skilled in the art from the foregoing detaileddescription of the invention. It is intended that all of thesevariations and modifications be included within the scope of the thisinvention.

1. A method for inhibiting replication of human hepatitis B virus incells in a human host in need thereof and infected with a hepatitis Bvirus comprising contacting the cells with an effective amount ofβ-L-thymidine of the formula:

or a pharmaceutically acceptable salt thereof.
 2. The method of claim 1,wherein the cells are contacted with an effective amount ofβ-L-thymidine of the formula:


3. The method of claim 1, wherein the cells are contacted with aneffective amount of a pharmaceutically acceptable salt of β-L-thymidineof the formula:


4. A method for the treatment of a hepatitis B virus infection in aninfected human host in need thereof and comprising administering to thehuman host an amount of β-L-thymidine of the formula:

or a pharmaceutically acceptable salt thereof, with a dosage effectiveto treat the hepatitis B virus infection by oral administration.
 5. Themethod of claim 4, wherein an effective amount of β-L-thymidine of theformula:

is administered.
 6. The method of claim 4, wherein an effective amountof a pharmaceutically acceptable salt of β-L-thymidine of the formula:

is administered.
 7. The method of claim 4, comprising administeringorally a unit dosage form of β-L-thymidine or a pharmaceuticallyacceptable salt thereof.
 8. The method of claim 7, wherein the unitdosage form comprises about 50-1000 mg of β-L-thymidine or apharmaceutically acceptable salt thereof.
 9. The method of claim 7,wherein the unit dosage form is a tablet.
 10. The method of claim 9,wherein the unit dosage form further comprises microcrystallinecellulose, gum tragacanth, gelatin, starch, lactose, alginic acid,Primogel, corn starch, magnesium stearate, Sterotes, colloidal silicondioxide, sucrose, saccharin, peppermint, methyl salicylate, or orangeflavoring.
 11. The method of claim 4, wherein β-L-thymidine or apharmaceutically acceptable salt thereof is administered at the dosageof about 1 to 20 mg/kg of body weight per day.
 12. The method of claim4, further comprising wherein β-L-thymidine or a pharmaceuticallyacceptable salt thereof is at least 95% in its designated enantiomericform.
 13. The method of claim 4, wherein the hepatitis B virus infectionis a chronic persistent hepatitis B virus infection.
 14. The method ofclaim 4, wherein the hepatitis B virus infection is a chronic infection.15. The method of claim 4, wherein the amount of β-L-thymidine or apharmaceutically acceptable salt thereof is effective to inhibit viralreplication in vivo.
 16. The method of claim 4, wherein the human hostin need thereof is anti-HBV antibody positive or HBV-positive.
 17. Themethod of claim 4, wherein the human host in need thereof has chronicliver inflammation caused by hepatitis B virus.
 18. The method of claim4, wherein the human host in need thereof has cirrhosis, acutehepatitis, fulminant hepatitis, chronic persistent hepatitis, orfatigue.